Help Needed - Electrical Issue

My stock radio unit has been acting up lately. It thinks I've turned on the lights when I haven't. I'll be driving along and then notice that the display has dimmed and the buttons illuminated as if I turned on my headlights / switched on parking lights. The display on the climate control is not affected, only the radio. I experimented a bit and noticed that when I actually turn the parking lights / head lights on and off, the radio display will brighten for a half second as if getting out of the dimmed mode but then will go back to dim.

With the parking lights off and I shut down the car, the dimmed radio will go back to normal (bright display) with the key now in the accessory position (1st turn of key). If turn the key to the on position (2nd click) the display remains bright (as it should). Now if I turn the the parking lights on, the display dims (as it should). But once I turn the parking lights off, the radio continues to be dim with buttons illuminated. Only when I turn the key back to the on position (1st click) the radio display brightens back up and the buttons are no longer illuminated. Obviously when I remove the key, everything is off.

What could be causing this?

Initially I thought the Android unit was causing the issue as I have a wire going from the stock illumination wire at the radio to the android illumination wire to let the Android unit know when to dim. I assumed the Android had an issue and was sending a signal back to the radio causing it to think I turned on the lights when I didn't. I have since disconnected the illumination wire but my issue persists. The only other wires on the stock radio that I've tapped into are constant power, switched power, and ground.

http://www.nsxprime.com/forum/showt...s-lights-are-on-but-they-are-not-Loose-switch



So after reading the above thread, I did some more experimenting. With the key in the on position (2nd click) and stepping on the brake pedal, when I turn the parking lights on, the radio buttons illuminate and the display dims (as it should). When I turn the parking lights off with my foot still on the brake pedal, the radio buttons stay illuminated and the display is still dim. Once I release the brake pedal, the radio buttons turn off and the display brightens.

I have the ARC Lights LED tails installed. Perhaps there's an issue with the light control box?

That post with the sneak circuit created by the tail / brake light bulb failure was truly bizarre; however, your problem may of may not be different. How is that for hedging a diagnosis. In the case of the bulb failure the sneak circuit was energizing the supply to fuse #38 which is normally controlled by the taillight relay / light switch. That fuse #38 circuit also provides the lights on signal to the CCU and clock and power to a bunch of other lights. The poster in that case noted that the climate control was dimming and other things were happening which is consistent with a strong sneak circuit (provides enough power to light up lots of stuff).

You only report problems with illumination on the radio, not the clock or the CCU which is a bit strange. However, it is possible that the detection circuit in the radio has a different detection threshold than the detection circuit in the CCU and clock. A high resistance in the sneak circuit may be limiting the sneak voltage such that the radio is switching; but, the other devices are not. If you have access to a voltmeter, and assuming you used the A3 red/blk wire on the radio for your illumination signal to the android device measure the voltage on that wire. With the lights on you should get a good 12 v signal. With the lights off it should be 0 v. If you do your brake light test with the lights off and you find that you get some intermediate voltage less than 12 volts, then you have a sneak circuit that is providing a voltage high enough to put the radio into dim mode (but, not trigger the CCU or clock).

I am not familiar with the ARC taillights; but, that would be a good place to start. The NSX taillight housings do have a bit of a reputation for suffering from moisture ingress and that contamination could have created a high resistance bridge allowing leakage between the brake circuit and the taillight circuit. Isolating the taillights and repeating the test to determine if the problem goes away would be a good way to determine if the sneak originates in the taillight assembly. Hopefully it does because a sneak circuit originating in the wiring harness could be a nightmare to find.

Good luck with it.

I’ve experienced this exact issue before and I’m still not 100% certain why it happens but I did manage to fix it.

In my case it started when I replaced the tiny bulbs in the cigarette lighter and ash tray with LEDs. It took me a while of troubleshooting to trace it back to that though, do you have burned out bulbs there or LEDs? I also found that unplugging the CCU made the issue go away.

What I found was that when the dimming circuit was supposed to be at 0V (lights off, backlights bright) it was actually floating at 3-4 volts with the LEDs due to their far lower current draw, the incandescent bulbs I replaced were acting as strong pull down resistors on the dimming circuit. I don’t know if this is by design or due to a fault in the CCU faceplate lighting (I could find no issues in the faceplate) but going back to incandescent bulbs in the lighter and ash tray fixed it.

I did not replace the cigarette lighter or ashtray lights. I just checked and I have no lights there. Maybe they're out, but honestly never noticed them before. I couldn't even tell where there would be a spot for a bulb. Did the 99s have bulbs there?

After more testing, my issue only occurs if the key is on (2nd click) position. I can't recreate it with the just in the accessory (1st click) position. Also, when the engine is off, I can only recreate the issue by turning the parking light switch on AND then stepping on the brake. If the engine is on, the issue can occur without me turning on the parking lights. Stepping on the brakes does seem to activate it. This leads me to believe that the higher voltage from the alternator generating power is increasing the sneak circuit to a level that activates the dimming feature on the radio.

I wonder if the jumper placed on the brake out warning sensor could cause this. Perhaps moving that to a dedicated ground may help.

When I have time I will have to remove he Arc Lights and put regular bulbs back to see if my issue will go away.

Also I noticed that when the engine is actually on, this issue can occur with or without me fir

I also only had the issue in the 2nd key position. But the brake pedal never seemed to have any affect on it in my car, it might be worth removing the jumper to see if it helps.

Yes 1999 cars have two bulbs, one for the cigarette lighter ring and one for the ash tray. You have to remove the console to get at them and it sounds like yours are burned out. Might be worth installing new bulbs.

MotorMouth93 said:

In my case it started when I replaced the tiny bulbs in the cigarette lighter and ash tray with LEDs. It took me a while of troubleshooting to trace it back to that though, do you have burned out bulbs there or LEDs? I also found that unplugging the CCU made the issue go away.

What I found was that when the dimming circuit was supposed to be at 0V (lights off, backlights bright) it was actually floating at 3-4 volts with the LEDs due to their far lower current draw, the incandescent bulbs I replaced were acting as strong pull down resistors on the dimming circuit. I don’t know if this is by design or due to a fault in the CCU faceplate lighting (I could find no issues in the faceplate) but going back to incandescent bulbs in the lighter and ash tray fixed it.

Click to expand...

It is correct that LEDs may present a very high resistance, essentially infinity if the voltage in the circuit is below the forward voltage of the diode. This can allow for 'floaty' voltages because the circuit has no other reference point. The common source for such indeterminate voltages would be a high resistance connection to an energized circuit, either through some failed insulation or some contamination that has created a high resistance conducting path to an energized circuit.

I won't deny your success with going back to incandescent bulbs; but, the dimming signal comes from fuse #38 and fuse #38 and #39 are tied directly together and there are a lot of lights on fuses #38 and #39 including the taillights, front position lights, rear side marker lights and license plate lights and a bunch of smaller lights. Unless you have changed all of those lights to LEDs, it seems odd that the conversion to LEDs on the cigarette lighter and ash tray is directly responsible for the problem. Having said that, I offer no alternate explanation for your problem.

Update: Problem solved!

Turns out when I recently changed my shift boot, I forgot to plug back in the cigarette lighter and temperature sensor. Once I plugged everything back in, my issue went away! Thanks guys for the suggestions! Saved me a ton of time troubleshooting as I was going to start with the Arc Lights.

Uh - I am not getting the connection between the cigarette lighter, temperature sensor and the supply for the radio dimming control; but, if it works don't kick the gift horse in the mouth! I am wondering if you had a flakey electrical connection to the radio dimming circuit which you inadvertently fixed when you did the other repairs.

Today all I did was plug back the cigarette lighter and temperature sensor. I didn't remove the radio or climate control.

No idea how it's all related but I'm happy.

The cigarette lighter power plug behind the console that you mentioned also powers the two light bulbs I suggested you check - it’s a 3 pin plug: ground, switched 12V for the lighter, and the dimming circuit which powers the 2 light bulbs. Do you by any chance have lights around the cigarette lighter and ash tray now?

Yes, I do have a light around the cigarette lighter! Never noticed before. Nothing for the ashtray. I assume it's burnt out but I'm not going to worry about it for now.

Any solution or more information on this?

I am migrating to all LED and the stereo is dimming when I press the brake when key is On (second position).

The the car is nearly nearly 100% LED with the exception of the instrument cluster and ancillary lamps inside the switches around steering wheel (conversion as opportunity permits). brake light failure sensor is bypassed as well as a modified flasher; everything is as it should be other than the stereo blinking off and on.

Seems like there is some relay clicking away on the rear bulkhead when the brake pedal is pressed that is involved too...

drew said:

Any solution or more information on this?

I am migrating to all LED and the stereo is dimming when I press the brake when key is On (second position).

The the car is nearly nearly 100% LED with the exception of the instrument cluster and ancillary lamps inside the switches around steering wheel (conversion as opportunity permits). brake light failure sensor is bypassed as well as a modified flasher; everything is as it should be other than the stereo blinking off and on.

Seems like there is some relay clicking away on the rear bulkhead when the brake pedal is pressed that is involved too...

Click to expand...

My issue was resolved once I plugged back in the cigarette lighter and aspirator fan. Not sure how the system is connected but they are.

Sent from my G5 using Tapatalk

In my case, the aspirator fan and lighter are hooked up. I can see the fan spinning with Key On and the ashtray+lighter lamps are illuminating.

What the brakes have to do with dimming is just strange...

Alright, this has gone on long enough: My android head unit display "disappears" during the daytime whenever I depress the brake pedal. Basically I cannot modify the settings when at a stop....which makes things difficult. I can use the e-brake, but this

I've looked at the schematics and I see no connection.

What is the theory of the brake dimming unit...how does it work?

How do I track this down:

Do I just start unplugging harnesses?

Measure the I/O of the dimming unit?

drew said:

What is the theory of the brake dimming unit...how does it work?

Click to expand...

Brake dimming unit? Is that a feature on RHD market cars because I don't ever recall seeing a reference to a brake dimming unit on my North American market car.

Are you using the A3 pin input (lights on) from the OEM stereo connector for your Android dimming control? If so, that input originates from the taillight relay output, specifically fuse 38. Fuse 38 supplies a bunch of stuff, headlight switch, dash light brightness control, glove box light .........input to pin A3 on the OEM stereo. With the headlights switched off, fuse 38 should have 0 volts. I suggest that you connect a voltmeter to fuse 38. With the ignition switch in Acc and your head unit switched on and headlights switched off you should measure 0 volts on fuse 38. Now press down on the brake pedal and check the voltage on fuse 38. Does fuse 38 remain at 0 volts and the head unit dims? If so, then something is amiss with the head unit itself or the connections to the head unit. If the voltage on fuse 38 rises above 0 volts (it may not have to be 12 volts to reach the dimness trigger threshold on the head unit) and the head unit goes dim, then you may have a sneak circuit between the brake circuit and the fuse 38 as there is no obvious direct connection between the two circuits. At that point, I think you have to start unplugging connectors and testing to find the source of the sneak.

In the 1991 service manual there is a connection from the brake switch output to the Integrated Control Unit. In my 1997-2000 electrical trouble shooting manual, a wire is shown going from the brake system monitoring circuit to the Integrated Control Unit; but, it is marked unused in the trouble shooting manual. Since you have an early car you might want to check to see if that connection is used for something in the ICU. The only reason I mention this is that the ICU gets tied back through the headlight switch to fuse 38. If something is up with the ICU it could be providing some kind of perverse high resistance sneak circuit back to fuse 38 and the head unit dimming control.

Other than the above, I am at a loss!

> If the voltage on fuse 38 rises above 0 volts (it may not have to be 12 volts to reach the dimness trigger threshold on the head unit) and the head unit goes dim, then you may have a sneak circuit between the brake circuit

I am getting 2.52V at Fuse 38 (ILLUMI LIGHTS) when the foot brake pedal is depressed.


The Brake circuit is pretty simple...two wires go into the brake switch (GRN/WHT - ABS/TCS/AT Controls and GRY (Cruise Control).

EDIT: GRN/WHT is the branch of the circuit that is affecting this issue.

I'm wondering if a resistor at A3 would knock this down?

drew said:

> If the voltage on fuse 38 rises above 0 volts (it may not have to be 12 volts to reach the dimness trigger threshold on the head unit) and the head unit goes dim, then you may have a sneak circuit between the brake circuit

I am getting 2.52V at Fuse 38 (ILLUMI LIGHTS) when the foot brake pedal is depressed.


The Brake circuit is pretty simple...two wires go into the brake switch (GRN/WHT - ABS/TCS/AT Controls and GRY (Cruise Control).

EDIT: GRN/WHT is the branch of the circuit that is affecting this issue.

I'm wondering if a resistor at A3 would knock this down?

Click to expand...

Are you talking about a resistor in series to the lights on connection (A3) on your head unit? If so, I don't think that will accomplish anything because the current flow into A3 is probably sub micro amp. If you are talking about a resistor connected between A3 and ground, that might work. Are you thinking of adding a resistor to ground that would drag the 'floaty' 2.52 volts down to a level that does not trigger the dimming circuit? The only potential concern I would have is that when you switch the headlights on input A3 goes solidly to 12 volts and current is going to be flowing through that resistor continuously. If the resistor needs to be a low value to drag the floating voltage to ground then the that resistor might get hot. You can experiment. If a 10,000 ohm resistor eliminates the floating voltage then the current during lights on will result in less than 0.02 watts losses and heating will be a non issue.

The other option to consider is a simple voltage divider. Connect a 10 k and 22k resistor in series to ground. Take the lights on signal from the mid point of the resistors which will give you a voltage of (10/(10+22))x2.52 = 0.787 volts. With luck this will be below the detection level of your lights on signal. If not, you can adjust the resistor sizes to drop the voltage more. The high resistance of the voltage divider circuit will result in miniscule current flow (< 0.2 ma) when the headlights are switched on.

It would be interesting to know where the coupling is occurring that lifts the voltage on fuse #38 when you apply the brakes.

It appears that <3V will activate the head unit's dimming circuit.

Tracking down the sneak circuit is going to be a lot of work. The next round of connectors are feeding the interior fuse panel and I'll have to depin them, one connector at a time, and test. Very time-consuming even if I get it on the first few tries. What is troubling is that @MotorMouth93 states that disconnecting the CCU will alleviate the problem too.

If I do figure out the issue, I presume it will require some hardware modification to fix.* I am reluctant to modify something original and only the head unit is seemingly affected...

Therefore, I intend to apply a hardware fix to patch the symptom**

The goal to reduce the A3 input by 3/4 (the legitimate input is 12V and will be dropped to 3V) to trigger the dimming into the head unit. With any luck, the voltage reduction will reduce the spurious sneak circuit voltage also by 3/4 and that will be below the threshold required to activate the dimming circuit.

My plan of attack is to use a voltage divider with 1:4 resistor ratio (9kOhm, Vout, 36kOhm) or use a step-down circuit board

By happenchance, I have a deck of 12V DC step-down boards from AliExpress for the NSX stereo project. So I will try these first as already have them and they are inexpensive (<$1 each); whereas a couple of packs of resistors will be more costly in time and money.


The big unknown is I don't know what the minimum voltage is required to trigger the dimming circuit on the radio. I am hoping that <=1v is below the threshold.


Comments are welcome.



*I'll continue looking as opportunity permits, but I don't think I'll be taking apart my interior fuse box for quite some years
**My CS professor will not be proud

keywords: radio stereo dim dimming brake pedal

Have you considered just disconnecting the dimming wire from the head unit? It will no longer dim but it should stay on at least. When I had my issue, the Android display never "disappeared" but simply dimmed.

You could also try a brute force approach of using a small PCB style SPDT relay. Connect the relay coil between the supply to pin A3 and ground. Connect the 'hot' side of the coil to one NO contact and the other side of the NO contact to the A3 input. 2.52 volts would normally be below the pull-in voltage for a 12 volt coil so the NO contact should stay open and completely isolate the A3 input and prevent dimming. When you switch on the headlights, the A3 input will go to >12 v, the relay will energize and apply 12 v to the A3 input causing it to dim.

Go to DigiKey and you can sort through the PCB relays to find one that has a high pull-in voltage. If you can't find a high pull-in voltage you could always add one or two 1n4001 diodes in series with the coil which would reduce the voltage to the coil.

Stereo dimming on brake update

I used a solid-state voltage reducer down to <3vdc and the stereo still dims when braking.

Looking like I'm forced into a mechanical relay as recommended by @Old_Guy, but I really don't want to add to the BSR every time I brake.

Here is the interesting part:
The brake to illumination "sneak circuit" does not occur on immediate Key On until the parking-/head- lights are turned on. Once the lights are turned on, and then off doesn't matter, pressing on the brake pedal will engage the "sneak circuit".

reproduce:
1. Turn ignition key to On. Radio on.
2. Press on brake pedal, notice the lack of radio dimming
3. Turn on parking or head lights. Note dimming of radio
4. Turn off parking or head lights. Note radio returns to full brightness
5. Press on brake, notice radio dimming in relation to brake application pedal up or down.
6. scream in exaspration.
UPDATE, working into the night which allowed me to observe that
7. the front park lights activate. (mine are converted to LED in the OEM housing sockets)

Also, the climate control unit and center console were not installed, completely detached, during my tests. So it would seem that the climate control, connections in the center console, or the clock are not directly involved in the issue.



Any ideas on what "switch" or relay is flipped or other contact is made when the parking or headlights lights are turned on for the first time?



/radio dimming on braking

drew said:

Stereo dimming on brake update

I used a solid-state voltage reducer down to <3vdc and the stereo still dims when braking.

Looking like I'm forced into a mechanical relay as recommended by @Old_Guy, but I really don't want to add to the BSR every time I brake.

Here is the interesting part:
The brake to illumination "sneak circuit" does not occur on immediate Key On until the parking-/head- lights are turned on. Once the lights are turned on, and then off doesn't matter, pressing on the brake pedal will engage the "sneak circuit".

reproduce:
1. Turn ignition key to On. Radio on.
2. Press on brake pedal, notice the lack of radio dimming
3. Turn on parking or head lights. Note dimming of radio
4. Turn off parking or head lights. Note radio returns to full brightness
5. Press on brake, notice radio dimming in relation to brake application pedal up or down.
6. scream in exaspration.
UPDATE, working into the night which allowed me to observe that
7. the front park lights activate. (mine are converted to LED in the OEM housing sockets)

Also, the climate control unit and center console were not installed, completely detached, during my tests. So it would seem that the climate control, connections in the center console, or the clock are not directly involved in the issue.



Any ideas on what "switch" or relay is flipped or other contact is made when the parking or headlights lights are turned on for the first time?



/radio dimming on braking

Click to expand...

I think that may be part of your issue. When I plugged the cigarette lighter and temperature sensor / aspirator fan back in, it solved my problem.

Ok, with that lead I am closing in: It is NOT the aspirator fan.

The symptom IS caused by the lack of an incandescent lamp in the ashtray. (there is a post on this somewhere) I installed an LED lamp in the ashtray and this is causing the unwanted dimming problem

There is a ~3.7vdc residual voltage that shows up after use of the parking- head- light switch. This voltage is dissipated with an incandescent lamp, but not enough energy to show any visible light.

I can replicate the issue--brake pedal down--, touch the leads of the incandescent lamp, and the front parking lights turn off and the dimming is gone.

Any insight on where to look next is appreciated.