How To Remove DRL Mod?

[Madhatter10-6]

I've spent hours searching forums, trying to figure out how my DRLs were wired, but I just can't seem to find the answer. Here’s what I know so far:

Vehicle Details:​

• 2005 Acura NSX (originally a U.S.-spec car)
• Imported to Canada, where a previous owner had DRLs installed to meet legal requirements
• Modification was done by a shop, and it was reportedly a quick process

Current Behavior:​

• No Key: All lighting functions operate normally—I have full control over low beams, high beams, and running lights. When I turn on the high beams BOTH the low and the high beams are on
• Key to On: The running lights and low beams turn on automatically. I can toggle the high beams on and off, but I have no control over the low beams. This information was wrong....it is JUST the low beams that come on...nothing else. But when I turn on the high beams BOTH the low beams and the high beams are on.

Troubleshooting So Far:​

• Fuse Position 3 (Cabin Fuse Box): Empty
• Interior Disassembled: I currently have most of the interior out for a stereo upgrade and sound deadening, but I haven't been able to locate where they tapped into the system.
• Fuse Boxes & Wiring: No visible modifications under the dash or in any fuse boxes.

I’d appreciate any help in tracking down where this mod was installed!

 

[MotorMouth93]

Start at the DRL fixtures and follow the wires from there....

 

[Madhatter10-6]

Start at the DRL fixtures and follow the wires from there....

Thanks helping point me in the right direction. When you say "DRL Fixtures" can you give me some additional clarity. Do you mean the actual DRL plugs at the front of the car?
(borrowed this pic from Honcho)

​

 

[MaxGeek]

Look under the front hood for non-oem looking wiring. On my car there is a relay that is apart of the DRL system. So perhaps yours has a similar setup and you can follow the wiring back to module. Also on my car just removing the relay works to disable the DRL's and the headlights still work normally.


On my car it's near the passenger side frame rail toward the radiator.

 

[comtec]

Is there a fuse in 41 or 44 of the under-hood fuse box?

 

[Madhatter10-6]

Is there a fuse in 41 or 44 of the under-hood fuse box?

From using this: https://www.startmycar.com/us/acura/nsx/info/fusebox/2005

and the FSM




There does not appear to be




On the startmycar.com diagram I think you are referring to locations 13 & U2
Those both appear empty on my car.

 

[Old Guy]

My car is an ex USDM 2000 and has a DRL modification a little bit like what you describe. The front running lights were used as the DRLs. Your car is a little bit unusual in that the low beams are also energized.

My installation might have been a little bit like MaxGeek's. The relay gets key-on power from the main front relay box (can't remember which fuse) with a separate 12v supply with fuse directly from the battery. The power from that relay intercepts the normal supply to the front running lights up front near the running lights so I have separate wires running from that relay located near the main relay box out to the right and left running lights. It was really a front running lights on all the time system because the lights would stay on even during engine cranking.

I don't have the SM or the electrical trouble shooting manual for the 2002+ cars which have significant modifications to the lighting system wiring because of the fixed headlight system. However, if the systems are similar I can do some guessing. Have you checked to see what your taillights are doing? If the taillights are on then you just have an 'all the lights on all the time whenever the ignition switch is on system'. On a pre 2002 car that would be very easy to implement. All you need to do is add a relay which applies a ground to the lighting relay and the taillight relay which switches everything on when the ignition key is in the run position. No need to add separate wiring down to the running lights. On early cars both these relays are in the main relay box up front so easy to access. You could gain control of the relays right close to the relays (where I have marked in blue in the diagram) or right at the lighting switch inside the car (where I have marked in red). All you need is a relay that grounds out these terminals at power up and voila, lights on all the time.




Assuming that the 2005 also has a lighting relay and a taillight relay you will need to find out where these are now located. This changed in later cars and I don't have the 2002+ electrical trouble shooting manual so you would need that to find out where those relays are located and look for non OEM wiring that would take you to the DRL relay. You could also check around the lighting switch looking for non OEM connections there.

If the taillights are not lit up then that is more complicated. You would need to add 'field' wiring to power up the front running lights independent of the taillight relay and that should be fairly obvious from poking around out front and that field wiring should ultimately take you to the DRL relay. Also, everything I have stated is based upon the 2005 being similar to the early cars wiring. If there were significant changes made to lighting control system wiring that changes everything.

 

[Madhatter10-6]

Old Guy...thanks for the very detailed write up! Unfortunately I made a mistake in my original description of the problem. I updated the first post to reflect this oversite:

Current Behavior:​

• No Key: All lighting functions operate normally—I have full control over low beams, high beams, and running lights. When I turn on the high beams BOTH the low and the high beams are on
• Key to On: The running lights and low beams turn on automatically. I can toggle the high beams on and off, but I have no control over the low beams. This information was wrong....it is JUST the low beams that come on...nothing else. But when I turn on the high beams BOTH the low beams and the high beams are on.

It looks like the shop has only set the low beam headlights to turn on when the key is in the ON position—nothing else. I apologize for the oversight.


That said, this seems like good news, right? Wouldn't this be a much simpler fix?

​

 

[comtec]

On the startmycar.com diagram I think you are referring to locations 13 & U2
Those both appear empty on my car.

No, according to the 97-05 ETM, Fuse 44 is the oem fuse for 97-01 DRL and fuse 41 is the oem fuse for 02-05 DRL . But they both look empty. Looks like their info is for the early cars.

 

[comtec]

Deleted, posted in wrong thread

 

[Wild Turkey]

Could we be on the wrong track looking at the OEM DRL wiring? No DRL on a 2005 USM NSX, & it seems unlikely the aftermarket shop would bother wiring it per OEM wiring for DRL's, with fuses in the correct location, gauge cluster indicator, etc. And the operation sounds much simpler than the OEM DRL, which won't activate DRL if the emergency brake is initially on. @Madhatter10-6 any E-brake effect? Gauge indicator? Operation at ignition I (Accessory)? Even less likely that an '05 has the wiring for the fog light look-a-like DRL's that came on '91-'01 NSX's shown in the pic in post 3.

It sounds like a relay triggered by the ignition-on 12V to either ground the headlight switch circuit or power the low beam circuits. They didn't just connect the headlights to the ignition power or the lights wouldn't work when the ignition is off, as they seem to. More likely grounding the supply side of the headlight relay, as they would have to tap into both the left and right headlight circuits and that would also be bypassing the fuses, so the taps would need to be fused as well. I expect it is like @MaxGeek's setup. Pretty much need to trace out the headlight switch circuit, then follow the headlight circuit back to the fuse box/relays. There must be a tap-in in one of them. Starting with the ignition-on or accessory-on circuits would take forever.

At the risk of sounding glib, why bother removing this? It's arguably safer & I doubt it weighs very much. Here are shots of from the 2002 electrical manual for assistance, which I think should be similar to 2005, but I'd recommend grabbing one for yourself, since it also has great pictures of all of the electrical connectors to help you locate them.




Edit: Was thinking about this waiting for a luncheon at church when I thought, "How would I add DRL to a fixed headlight NSX?" There are +, acc+, Ign+ and ground spades just above the fusebox near the driver's door. I'd put a relay there, with the trigger wired to the ign+ & ground, and the switched leads connected to ground and run to red/blu, either at C416 (bottom of the steering column) or perhaps C243 (behind right kick panel.) See page 100-5 above.

 

[Old Guy]

To confirm your update, the running lights do not come on as part of the DRL function? If so, that does simplify things a lot. It also makes sense. If the low beams are on why bother with operating the running lights because they will have minimal effect in terms of improving the cars forward facing visibility.

With the diagrams from @Wild Turkey, it would be very easy to implement this function. All you need to do is switch on the headlight low beam relay by applying a ground to pin 2 of the relay (diagram on page 100-5). I expect a simple SPST external relay to apply this ground to the low beam relay. The external relay would be powered up in the ignition switch on position and there are probably 100 places in the car where you can pick an ignition on condition so it is impossible to be definitive about that. This may be 'enhanced' a bit if the low beams shut off during cranking; but, that fundamentally doesn't change the fact that the switching is probably being done at the low beam relay terminal 2. So, if you want to remove the function, I would start at the low beam relay and look for a foreign wire added to the red/blue wire on terminal #2 of the low beam relay and follow that wire to wherever. The connection has to be made before the 'headlight diode' otherwise the DRL function will interfere with the high beam operation.

As an observation, as Wild Turkey has suggested, if the installation is tidy I would be inclined to leave it alone. In Canada, DRLs have been a thing since the late '80s. That is long enough that the majority of drivers have not experienced cars without DRLs and I find that most people have now become conditioned such that if the headlights or DRLs are not on, the car is not perceived as moving. I have a vintage Volvo and I added a DRL function to the headlights because people did not perceive it as moving even though it was firmly in the driving lane and is not a small car. This led to some pull into the path events because 'they did not register the car as moving'. The US was late to the DRL game and that conditioning may not have occurred (yet); but, my opinion is that the NSX has a small frontal profile and needs all the help it can get in terms of making people mentally aware of its presence. Flashing red and blue lights would probably be effective . When I got my car USDM car it had a minimalist installation using the running lights as DRLs. I went out and purchased some dedicated much brighter LED based DRL strips to make the car's presence more obvious.

Your car, your choice.

 

[Madhatter10-6]

To confirm your update, the running lights do not come on as part of the DRL function? If so, that does simplify things a lot. It also makes sense. If the low beams are on why bother with operating the running lights because they will have minimal effect in terms of improving the cars forward facing visibility.

Correct...just the low beams

So to make sure I am understanding you correctly:



Pin 2 (Circled in Red) is getting a bonus ground sent to it in order to arm that relay and turn on the low beams?

AND

That bonus ground is occurring on the red blue wire before the head light diode on the section that I have in GREEN?

It looks like that is before the C251 connection?

Thanks so much for the help with this!

 

[Madhatter10-6]

Edit: Was thinking about this waiting for a luncheon at church when I thought, "How would I add DRL to a fixed headlight NSX?" There are +, acc+, Ign+ and ground spades just above the fusebox near the driver's door. I'd put a relay there, with the trigger wired to the ign+ & ground, and the switched leads connected to ground and run to red/blu, either at C416 (bottom of the steering column) or perhaps C243 (behind right kick panel.) See page 100-5 above.

Great idea...and I will look into that ASAP

Also thanks so much for taking the time to post the sections of the manual and help think through all of this!

 

[Madhatter10-6]

So I was able to look around in the driverside footwell area again at what I believe are C416 and C243 and nothing.

Pretty sure this is C416



and I didn't see anything above or behind the fuse box

 

[Old Guy]

That bonus ground is occurring on the red blue wire before the head light diode on the section that I have in GREEN?

It looks like that is before the C251 connection?

Thanks so much for the help with this!

That is correct. The C251 connector probably looks like one of those in line fuse holders with a diode instead of a fuse.

This connection point appears to be functionally identical to what Wild Turkey suggests. The difference is on which side of the headlight diode the switched ground is applied. Wild Turkey's suggestion would appear to exactly replicate the operation of the low beam headlight switch.

The 2002 lighting control system is even more convoluted than the early cars having a high beam relay, low beam relay and a dimmer relay. My comment

The connection has to be made before the 'headlight diode' otherwise the DRL function will interfere with the high beam operation.

is probably incorrect. It is hard to suss out what the function of the headlight diode is by hopping from page to page on the photos attached by Wild Turkey and I am not prepared to invest the time to print out the pages and connect the dots to try and figure out what is going on since I have no skin in this game. It is possible that the switched ground could be applied anywhere on that red/blue wire and it should switch the low beam relay on. Of course, the installer could have done something completely different. We merely point out easy ways that it could have been done and a good place to start looking.

 

[Madhatter10-6]

Been testing this AM and they have 100% used this point to trigger

Whats interesting is that the relay clicks when the key is off and arms that relay....but in the key on position the lights are already only and the relay still clicks when I arm it with the switch.

 

[Wild Turkey]

I see nothing is connected to the accessory spades above the fusebox, where I would have done it. I'm interested in how you were able to be 100% sure they used that point to trigger the lo-beams as DRL. If they did, the ignition-on would trigger the relay and it should stay triggered as long as the ignition is on, and not switch with the headlight switch. Thus, the relay switching on and off with the headlight switch while the lights remain on with the ignition on suggests the opposite, that they are not grounding the red/blu, unless your high beams are also on and it's the high beam relay that's switching/clicking.

Diagnostic (Ignition on means key to on, without starting):

1. Double check to be sure you are identifying the high and low beam relays correctly. Perhaps remove the high beam relay if there is any chance of confusion.
2. Turn the key to accessory and verify that the headlights do not come on. If they come on at accessory, there will be a different diagnosis tree.
3. Check that turning the ignition to on without starting the car still activates DRL. If the lo-beams come on as DRL only when it's running, they are using a DRL module that will require different diagnosis.
4. Check that turning the ignition to on with the e-brake engaged still activates DRL. If the lo-beams come on as DRL only when the e-brake is disengaged, they are using a DRL module that will require different diagnosis.
5. With the headlight switch off, turn the key on and then off and see if you can feel the lo-beam headlight relay click as the key turns on and off. If so, that means the DRL is grounding the red/blu wire between the headlight switch and the relay box. (In that case, switching the headlight switch with the ignition on should not make the relay click as the ignition+ should be keeping it triggered.) Trace the RED/BLU from the headlight switch to the fusebox. The DRL is tapping in somewhere to ground it, probably with a relay triggered by the Ignition on.
   1. If not, DRL probably isn't grounding the red/blu anywhere, let alone at 2 where circled.
6. Headlight switch off: Remove the lo-beam relay and turn the ignition on. If the lights come on, this is evidence that the DRL is being activated after the relay.
7. If lights come on without the relay, pull the headlight fuses. If this stops them from coming on, the DRL tap is in the fusebox, between the relay and the fuses.
8. If they still come on without the fuses, DRL is tapping in after the fuses. Trace the wiring from the relay box to the headlights. There must be a (hopefully fused) 12V DRL tap-in on the RED/YEL and the RED/GRN going from the relay box to the headlights.
9. If the relay is required for the DRL to work, this suggests that that the system is grounding the red/blu somewhere, but then you should hear the relay click with ignition switch, and when it is on, the headlight switch should have no effect on the relay to cause clicking, because it is already triggered by the ignition+, presumably grounding the red/blu.

 

[Madhatter10-6]

I see nothing is connected to the accessory spades above the fusebox, where I would have done it. I'm interested in how you were able to be 100% sure they used that point to trigger the lo-beams as DRL.

Wild Turkey, awesome logical breakdown—thanks so much for taking the time to do this!

To answer the question above, I pulled the headlight low beam relay.

• Key out: Side markers work, high beams work, but low beams don’t. However, when I switch the low beams on, pin #2 goes to ground (tested with a test light).
• Key ON (relay still removed): All headlights turned off, and pin #2 returns to ground as soon as the key goes to on.

Based on this, I believe this confirms that pin #2 is the grounding control point for the relay.


Do you agree?

Starting on the rest of your post now

 

[Madhatter10-6]

Diagnostic (Ignition on means key to on, without starting):

1. Double check to be sure you are identifying the high and low beam relays correctly. Perhaps remove the high beam relay if there is any chance of confusion.

Smart to make sure we are all on the same. This is the relay that I think is the high beam...when removed...high beams turn off. Removing it changes none of the other functions in any of the key states.



#2

Turn the key to accessory and verify that the headlights do not come on. If they come on at accessory, there will be a different diagnosis tree.

Verified....accessory = no headlights automatically coming on (low or high) zero state change.

-----------------------------------------

#3

Check that turning the ignition to on without starting the car still activates DRL. If the lo-beams come on as DRL only when it's running, they are using a DRL module that will require different diagnosis.

The low beams come on as soon as the key is turned to ON without starting the car

-----------------------------------------

#4

Check that turning the ignition to on with the e-brake engaged still activates DRL. If the lo-beams come on as DRL only when the e-brake is disengaged, they are using a DRL module that will require different diagnosis.

E-brake status plays zero role in lights behavior

-----------------------------------------

#5

With the headlight switch off, turn the key on and then off and see if you can feel the lo-beam headlight relay click as the key turns on and off. If so, that means the DRL is grounding the red/blu wire between the headlight switch and the relay box. (In that case, switching the headlight switch with the ignition on should not make the relay click as the ignition+ should be keeping it triggered.) Trace the RED/BLU from the headlight switch to the fusebox. The DRL is tapping in somewhere to ground it, probably with a relay triggered by the Ignition on.

1. If not, DRL probably isn't grounding the red/blu anywhere, let alone at 2 where circled.

Yes...with headlights turned off and the key cycled on / off = clicking in relay

Key turned to on....THEN cycling the headlight controls = no additional clicking of that relay

However the reverse is NOT true.

If I first set headlights to low beam on there is one initial click at the relay
but when I cycle key from off to ON there is an additional click in that relay

-----------------------------------------

#6

Headlight switch off: Remove the lo-beam relay and turn the ignition on. If the lights come on, this is evidence that the DRL is being activated after the relay.

Headlight switch off, lo beam relay removed ignition turned to on = no lights coming on.

-----------------------------------------

#7

If lights come on without the relay, pull the headlight fuses. If this stops them from coming on, the DRL tap is in the fusebox, between the relay and the fuses.

Didn't come on so NA

-----------------------------------------

#8

If they still come on without the fuses, DRL is tapping in after the fuses. Trace the wiring from the relay box to the headlights. There must be a (hopefully fused) 12V DRL tap-in on the RED/YEL and the RED/GRN going from the relay box to the headlights.

Headlights on / key off = when I pull fuses the corresponding headlight turns off

Headlights off / key on = when I pull fuses the corresponding headlight turns off

-----------------------------------------

#9

If the relay is required for the DRL to work, this suggests that that the system is grounding the red/blu somewhere, but then you should hear the relay click with ignition switch, and when it is on, the headlight switch should have no effect on the relay to cause clicking, because it is already triggered by the ignition+, presumably grounding the red/blu.

Yes the relay is required for the DRL to work

That is correct.....and also my assumption.

Once again for clarity the relay situation is odd....see response to #5 above


Also thanks again for the time to help an internet stranger out with this level of detail!

 

[Madhatter10-6]

Also the original owner of the car found the reciept of the shop that did the work. I called them today and they still had notes on the install but the tech was no longer there.

Their notes said something to the effect of: Customer came in wanting DRL, did wiring inspection and installed fused relay under the box

So that does seem to be how this is being triggered

 

[Wild Turkey]

How are you verifying that it goes to ground? Test light connected to 12V+ on one side and the other side to the test lead? Note that your test does not confirm that Pin2 is the connection point, only that Pin2 is connected to the connection point. The tap-in point could be anywhere along the RED/BLU.

5 is perplexing. The only thing I can think of is a 3-way relay interrupting the RED/BLU wire, switching the RED/BLU (=> relay) away from the RED/BLUE (=> headlight switch) to a pure ground. This would result in one click turning the ignition on, and then no clicks from the headlight switch while the ignition remains on. But if the headlight switch was on, you could still get a click from the headlight relay when the ground is lost for a millisecond while the added DRL relay switches from the headlight-switch ground to the DRL ground.

Either way, if you're sure it's going to a good ground as in paragraph 1, I'm convinced the relay must be tapping in on the RED/BLU somewhere between the headlight switch and the relay box, so follow those wires carefully. There has to be a connection in there somewhere. Under the fuse box perhaps, based on the old notes?

 

[Madhatter10-6]

Not sure if this is relevant or not...but there is a brown 4 pin connector in the passenger floor board
If I disconnect it 100% normal functionality is restored
but critical power to my Haltech and a lot of the rest of the car is lost

Not sure if this helps in the the possible location process

 

[Madhatter10-6]

How are you verifying that it goes to ground? Test light connected to 12V+ on one side and the other side to the test lead? Note that your test does not confirm that Pin2 is the connection point, only that Pin2 is connected to the connection point. The tap-in point could be anywhere along the RED/BLU.

Yes. Test light wire to battery positive post....then I used the pointed test in to light up when it received ground. And it did from both the head light switch and just the key to on.

Also agreed about it being anywhere to tap in.

5 is perplexing. The only thing I can think of is a 3-way relay interrupting the RED/BLU wire, switching the RED/BLU (=> relay) away from the RED/BLUE (=> headlight switch) to a pure ground. This would result in one click turning the ignition on, and then no clicks from the headlight switch while the ignition remains on. But if the headlight switch was on, you would still get a click from the headlight relay when the ground is lost for a microsecond as the added DRL relay switches from the headlight-switch ground to the DRL ground.

Agreed. That makes sense.

ither way, if you're sure it's going to a good ground as in paragraph 1, I'm convinced the relay must be tapping in on the RED/BLU somewhere between the headlight switch and the relay box, so follow those wires carefully. There has to be a connection in there somewhere. Under the fuse box perhaps, based on the old notes?

Agreed... I just don't know that UNDER the fuse box means. I have looked everywhere and just don't see it.

 

[comtec]

Not sure if this is relevant or not...but there is a brown 4 pin connector in the passenger floor board
If I disconnect it 100% normal functionality is restored
but critical power to my Haltech and a lot of the rest of the car is lost

Not sure if this helps in the the possible location process




View attachment 198662

The pin 2 blue/red stripe wire at the low beam relay should be in the 16-pin blue connector under that one. In position 6 of the connector (latch side ,one from the end). See if anything is attached to it in the area. Maybe under the box meant behind the glove box.