Fuse 38 keeps blowing! Needs some help.

[TitaniumVtec]

I spent about 6 hours yesterday going over a friend's 91 NSX, trying to figure out why his Illumination fuse keeps blowing. He said it just blew one evening while driving around. Nothing out of the ordinary was taking place like rain, bumpy road, etc. (which shouldn't matter anyway).

I pulled out the service manual and check out the schematic on page (23-56). This illustration clearly shows that the power from the batter passes through the Taillight Relay before energizing the number 38 wire. The problem clearly exists after the relay, as this relay also provides power to the number 39 fuse/wire (L. Taillights). Both 15 amps I might add.

I find it strange that the number 39 fuse supports only the left rear taillights, while the 38 fuse supports the following:

R. Taillights
Front and side parking lights
License plate lights
Dash brightness control unit & controller
Hazard switch lights
Lighting switch lights
Power mirror/door locks switch lights
Rear defogger switch light
Cruise light
TCS switch light
Stereo radio/cassette dimming lights
Clock
Glove box light
Cigarette lighter light
Gauge lights
Ashtray lights
Automatic climate control switch lights

I removed the center console, a/c controller and clock. I disconnected the dimmer control unit behind the drivers seat. I disconnected the R Taillight harness in the trunk. I disconnected the license plate harness also. None of these things made a difference. The fuse just blew immediately.

I looked at some of the other pages in the manual and did not see anything that really could be causing a problem other than a short (wire touching metal someplace). Anyone have any clues as to how I should attempt to trace this problem? I have more than enough knowledge (I think??) to do it, but my problem is how do I start? I sure would hate to have to follow the 38 wire from the fuse box inside the car. But hey, would said this was going to be easy??

One small note. Before we started, some times a fuse would last for a minute or so before blowing. However, once the circuit heated up, the next fuse installed blew immediately. If we let the car sit for 30 minutes a fuse would hold again for a short time. One time, a fuse lasted for at least 10 minutes. I thought I had figured out the problem before it blew again. After that point, we were never able to make a fuse last for more than a second. Like something was really messed up now.

Thanks in advance,
James

 

[Larry Bastanza]

WOW,

This is a lot to think about. You have made is very clear to me why the rear tail lights in most NSX's seem to have a different brightness though.

I would say you still need to disconnect things further. If you can get a DVM, WITH THE BATTERY DISCONNECTED, measure the resistance from the output side of the fuse holder (With no fuse in place this should be 0 volts WITH the battery connected.

Also I would look very carefully for any collision damage. This is when these kind of problems usually arise, or if any aftermarket gizmo's may have been installed. Also check all the exterior lighting for places that water can get in and corrode things, or stay laying around. Sometimes it is easier to look with your eyes, then with a meter.

Sorry I cannot offer any more concrete ideas.

HTH,
LarryB

 

[TitaniumVtec]

Thanks Larry.

This NSX has been in 2 medium-size front end accidents. Its just that those events happened several years ago. I would not have thought about it again until you mentioned it. I will hunt this bastard down or pay someone else to do the dirty work. ha, ha More searching is on the way it appears!!

Thanks again,
James

 

[Cees-Jan]

Sometimes when a light bulb blows, the two connecting wires inside the bulb are melted toghether, Is the fuse melting with lights on or off??

Not a very elegant but working method is putting in a 20 amp fuse and measure the amount off amps, see if it stays in there,In vorklifts i have seen mechanics shortcircuiting the fuse, and after this the smoke is the location of the problem.......(dont try this)

 

[NCC-1701D]

Maybe check the wire loom and wires that are in the door and where the doors hinges are...Maybe opening and closing the doors over time wore some of the protective cover over the wires and exposed them to metal..

 

[heretic]

What about the relays???
Just for S & G replace them.

 

[D'Ecosse]

Sometimes when a light bulb blows, the two connecting wires inside the bulb are melted together, Is the fuse melting with lights on or off??

This was my first thought also - it has to be occurring when the lighting relay is energized i.e. the light switch is on - there most likely will be a bulb that is causing this - also check the side marker lights & front position lights that also come from this fuse.

I'd personally rather be trouble-shooting while it is blowing consistently - when it does it once a week you have little chance of finding, but this way, you just need to keep disconnecting things until it goes away - rather than going one part at a time, try to break it into chunks, then when you find a chunk that affects the result, then split that. This is known as half-split technique - i.e. disconnect half of the harnesses - if it doesn't change, problem must be in other half (or if it is then reconnect half of the original set); then break the next set sequentially again into two & keep going till you isolate the problem.
Good Luck!

 

[D'Ecosse]

What about the relays???
Just for S & G replace them.

Relay is before the fuse so not the problem

 

[cparsons]

I spent about 6 hours yesterday going over a friend's 91 NSX, trying to figure out why his Illumination fuse keeps blowing. He said it just blew one evening while driving around. Nothing out of the ordinary was taking place like rain, bumpy road, etc. (which shouldn't matter anyway).

I pulled out the service manual and check out the schematic on page (23-56). This illustration clearly shows that the power from the batter passes through the Taillight Relay before energizing the number 38 wire. The problem clearly exists after the relay, as this relay also provides power to the number 39 fuse/wire (L. Taillights). Both 15 amps I might add.

I find it strange that the number 39 fuse supports only the left rear taillights, while the 38 fuse supports the following:

R. Taillights
Front and side parking lights
License plate lights
Dash brightness control unit & controller
Hazard switch lights
Lighting switch lights
Power mirror/door locks switch lights
Rear defogger switch light
Cruise light
TCS switch light
Stereo radio/cassette dimming lights
Clock
Glove box light
Cigarette lighter light
Gauge lights
Ashtray lights
Automatic climate control switch lights

I removed the center console, a/c controller and clock. I disconnected the dimmer control unit behind the drivers seat. I disconnected the R Taillight harness in the trunk. I disconnected the license plate harness also. None of these things made a difference. The fuse just blew immediately.

I looked at some of the other pages in the manual and did not see anything that really could be causing a problem other than a short (wire touching metal someplace). Anyone have any clues as to how I should attempt to trace this problem? I have more than enough knowledge (I think??) to do it, but my problem is how do I start? I sure would hate to have to follow the 38 wire from the fuse box inside the car. But hey, would said this was going to be easy??

One small note. Before we started, some times a fuse would last for a minute or so before blowing. However, once the circuit heated up, the next fuse installed blew immediately. If we let the car sit for 30 minutes a fuse would hold again for a short time. One time, a fuse lasted for at least 10 minutes. I thought I had figured out the problem before it blew again. After that point, we were never able to make a fuse last for more than a second. Like something was really messed up now.

Thanks in advance,
James

Wow, bringing up a REALLY old thread!...

Did you get this fixed? What was the solution?

 

[TitaniumVtec]

The problem ended up being a short in the left front parking light. One of the bumper supports for his after market bumper lost a nut. This caused the bumper to sag a little and the parking light wire was pulled taut and started to rub on some sheet metal.

We added the nut back, shielded the wire with electrical tape and all as been well since.

James

 

[cparsons]

The problem ended up being a short in the left front parking light. One of the bumper supports for his after market bumper lost a nut. This caused the bumper to sag a little and the parking light wire was pulled taut and started to rub on some sheet metal.

We added the nut back, shielded the wire with electrical tape and all as been well since.

James

Great result and glad to hear it's working well. Thanks for the response!

 

[cparsons]

I have a fuse that keeps blowing every time I turn the lights on. I think it's also number 38. Is there a chart to check for sure? Its a 15A near the top of the box underneath the hood. The top of the box says ILUM/TAILLIGHT. This fuse pops every time I turn my lights on. Does anyone have any idea why or how to diagnose/fix?

For further info, I recently replaced an aftermarket stereo with another aftermarket stereo. I kept the same harness and didn't run/cut any new wires. The timing lines up with the stereo install, but I can't think of anything I changed to cause this.

Thanks for any help!

 

[ralph cerbone]

ok guys i will try to keep this as simple as possible , do the basic checks first ,has car been hit or repaired,if not the easiest way to find a short to ground (blows fuse ) is to test it while it is happening, ok how do i do that if it blows the fuse everytime i turn on the function ???? a simple circuit consist of a battery -- fuse--- switch---load ( light or motor) , when you have a short that blows the fuse it means the power is going to ground after the fuse and before the load (hence short circuit) , you now have power at one side of the fuse holder and ground at the other side of the fuse holder , now wire a light bulb ( or when i am by myself i use a alarm buzzer), into the fuse receptacle , turn it on,if it the short is active the light or buzzer will come on , now the quest is to turn it off, you must know what circuits the fuse controls , 1st split those circuits (even if you have to cut a wire, solder repair later ) once the shorted circuit is identifyed ,move the harness ,when the short is cleared the light will go off , you can disconnect all the lights and motors in a circuit but if the short is before the load such as a pinched wire this is the way to find it this is how i was taught almost 40 yrs ago , and how i instruct for the last 15 yrs,

 

[warren1205]

Wow! if i would have read this earlier i could of told you that. The exact same thing happen to me. EXACTLY THE SAME THING! drove me nuts trying to trace the short. Im glad you addressed the issue.

 

[cparsons]

ok guys i will try to keep this as simple as possible , do the basic checks first ,has car been hit or repaired,if not the easiest way to find a short to ground (blows fuse ) is to test it while it is happening, ok how do i do that if it blows the fuse everytime i turn on the function ???? a simple circuit consist of a battery -- fuse--- switch---load ( light or motor) , when you have a short that blows the fuse it means the power is going to ground after the fuse and before the load (hence short circuit) , you now have power at one side of the fuse holder and ground at the other side of the fuse holder , now wire a light bulb ( or when i am by myself i use a alarm buzzer), into the fuse receptacle , turn it on,if it the short is active the light or buzzer will come on , now the quest is to turn it off, you must know what circuits the fuse controls , 1st split those circuits (even if you have to cut a wire, solder repair later ) once the shorted circuit is identifyed ,move the harness ,when the short is cleared the light will go off , you can disconnect all the lights and motors in a circuit but if the short is before the load such as a pinched wire this is the way to find it this is how i was taught almost 40 yrs ago , and how i instruct for the last 15 yrs,

Thanks, Ralph. After reading your message a few times I have better understanding of how it works.

I'm going to take the console back apart, check my work and try to find that ground.

Does anyone out there have a similar experience? Is there any common wire/place to check?

 

[ralph cerbone]

casey, when ever i have to fix these types of problems i spend most of the time looking at the electrical print ,then the piece of equiptment, when dealing with cars i look very closlely if any work has been done( body or mechanical), i trust no one, many times a tech or owner will do a fundamental service or repair and for whatever reason this can lead to a headache, (like pinching a wire after replacing a taillight assm., or the infamous golf clubs in the trunk) be patient you'll be fine

 

[cparsons]

Update: I took apart the console and dash earlier this afternoon. I disconnected and removed the clock, climate control unit and cigarette lighter and miraculously and the fuse didn't pop when I turned on the lights. The dash lit up and the right rear tail light stayed lit! I ran out of time but in the next few days I plan to reconnect the clock, CCU and lighter one at a time to determine which unit (or wiring) is having the issue.

So, I still don't know exactly what the cause is or how to fix it but I am a step closer.

Thanks for the help and advice!

 

[cparsons]

Update: Fixed! I disconnected the clock, CCU and cigarette lighter and the fuse did not pop anymore. Then plugged each in separately and none caused the fuse to pop. Then plugged them all in at the same time, and still the fuse didn't pop. So, I just put everything back together and it all works fine. My best guess is that a wire was pinched from last week's install. Thanks!

 

[EuroBoutique]

I know this is a very old thread but most useful info on Fuse 38 and 39!

So I got a small dilemma maybe you guys can give me some input.

Fuse 38 is not blown, nor has it ever blown but it seems the parking lights do not work and everything associated with Fuse 38 does not power up either. I tried replacing the fuse just in case but the car has no parking lights

However Fuse 39 (Left taillight) works just fine.

 

[EdinKali]

Most likely the relay for that circuit. Check the connection(s) for that relay and if they look ok, replace the relay. The other possibility is that part of the switch has gone bad(might be able to take it apart and clean the contacts). My money is on the relay.

 

[EuroBoutique]

Most likely the relay for that circuit. Check the connection(s) for that relay and if they look ok, replace the relay. The other possibility is that part of the switch has gone bad(might be able to take it apart and clean the contacts). My money is on the relay.

Thanks for the tip! Which relay do you suggest? I already looked at the

Lighting relay
Tail lights relay

(Both above fuse 38)

I also hear it click when I turn to the first position.

Thanks again

 

[warrenw]

I know this is a very old thread but most useful info on Fuse 38 and 39!

So I got a small dilemma maybe you guys can give me some input.

Fuse 38 is not blown, nor has it ever blown but it seems the parking lights do not work and everything associated with Fuse 38 does not power up either. I tried replacing the fuse just in case but the car has no parking lights

However Fuse 39 (Left taillight) works just fine.

There is a junction at the front marker lamp. Power, in-> power out. from park lamp supply to rear and side marker lamps. Pull the front marker lamp on that side of the car. the wires are short and when replacing bulbs a tendancy is to pull on them and possibly dammaging the red/black wire connection. You will see two red/black wires and a ground to the front park lamp. You will need to check the connection at the bulb socket.

2 cdn cents.

 

[EdinKali]

Thanks for the tip! Which relay do you suggest? I already looked at the

Lighting relay
Tail lights relay

(Both above fuse 38)

I also hear it click when I turn to the first position.

Thanks again

Might as well replace both, they are cheap(6 or 7 bucks a pop at your local auto parts store if it is a common Honda/Acura relay). If it doesn't fix the problem, at least you have ruled them out.