Ok...Check this out..Tonite I get into my 1991 nsx..It's starts up just fine, I put the headlights on and NO headlights...All the other lights are working fine. So with the headlights still on, I Shut the car off and now the head lights come on (very dim) but the dash lights go off. So again, I start the car and again the headlights go off and the dash lights come on. I did this a couple of times and now the headlights wont come on at all, all others do...Someone please tell me, this is a easy fix, like maybe a relay or something.
-
Protip: Profile posts are public! Use Conversations to message other members privately. Everyone can see the content of a profile post.
Lights are Going wacky
- Thread starter RMFOR2
- Start date
I just looked at the headlight circuit in the 1995 ETM (electrical troubleshooting manual), and its interesting, to say the least. There's also some details left out, but I think I've figured that out 
.
Looking at the upper left corner of the box (as viewed when you are looking from the front bumper), the relays are:
Power window Relay Taillight Relay
(small) (small)
Dimmer Relay Headlight Relay
(largest relay) (about 2/3 the size of the
dimmer relay)
I believe there is also a diagram in the cover of that box.
The dimmer relay switches high/low beam. Here's where the schematic is missing a few details, but it looks like both bulbs get +12V, and this relay switches ground to the correct headlight bulb(s).
The headlight relay switches power to the headlights.
It looks like if your high/low beam switch on the stalk & flash-to-pass switch are totally screwed up, you should at least get low beams.
Fuses 49 & 52 (just below the dimmer relay) are 20 amp fuses for the right and left headlights, respectively.
The headlight relays are directly (no fuse before them) connected to +12V at all times.
Things I would try:
1. Let's start with the simplest test. Try flash-to pass and see if that works. The headlights should come on, even with all swiches off and no key in the ignition.
2. If that doesn't work, check fuses 49 & 52 with an ohmmeter or turn the headlight switch turned on and try a replacement 20A fuse. Next, if you have a voltmeter, with the headlight switch on, check for +12V at the fuse to ground (via the little hole in the top of the fuse.
3. If there's no 12V, then the headlight relay is suspect.
or
4. If there is 12V, a bad ground at the headlights or the dimmer relay is suspect.
Let me know if you have a multimeter and how well you can use it. We'll try further tests from there.
My wife & I are busy preparing for a large family breakfast gathering tomorrow. Once the crowd clears, if you haven't had luck by the afternoon, I can scan or photograph pages 6, (fuse/relay box) and 100 thru 100-4 of the ETM and send them to you.
There are are all sorts of grounds that can go bad and mess up things, so lets try the easier stuff first, and then work through the trickier stuff if needed.
. Looking at the upper left corner of the box (as viewed when you are looking from the front bumper), the relays are:
Power window Relay Taillight Relay
(small) (small)
Dimmer Relay Headlight Relay
(largest relay) (about 2/3 the size of the
dimmer relay)
I believe there is also a diagram in the cover of that box.
The dimmer relay switches high/low beam. Here's where the schematic is missing a few details, but it looks like both bulbs get +12V, and this relay switches ground to the correct headlight bulb(s).
The headlight relay switches power to the headlights.
It looks like if your high/low beam switch on the stalk & flash-to-pass switch are totally screwed up, you should at least get low beams.
Fuses 49 & 52 (just below the dimmer relay) are 20 amp fuses for the right and left headlights, respectively.
The headlight relays are directly (no fuse before them) connected to +12V at all times.
Things I would try:
1. Let's start with the simplest test. Try flash-to pass and see if that works. The headlights should come on, even with all swiches off and no key in the ignition.
2. If that doesn't work, check fuses 49 & 52 with an ohmmeter or turn the headlight switch turned on and try a replacement 20A fuse. Next, if you have a voltmeter, with the headlight switch on, check for +12V at the fuse to ground (via the little hole in the top of the fuse.
3. If there's no 12V, then the headlight relay is suspect.
or
4. If there is 12V, a bad ground at the headlights or the dimmer relay is suspect.
Let me know if you have a multimeter and how well you can use it. We'll try further tests from there.
My wife & I are busy preparing for a large family breakfast gathering tomorrow. Once the crowd clears, if you haven't had luck by the afternoon, I can scan or photograph pages 6, (fuse/relay box) and 100 thru 100-4 of the ETM and send them to you.
There are are all sorts of grounds that can go bad and mess up things, so lets try the easier stuff first, and then work through the trickier stuff if needed.
Last edited:
It was stated the car starts fine. The starter draws a few hundred amps; the 4 headlights draw less than 40 amps total. My guess would be the battery terminals are fine. However, checking and cleaning them never hurts.
Page 23-78 of the shop manual: "use a 0-400A Ammeter"
Page 23-79 of the shop manual: step 4, checking cranking current, "current should be no more than 350 amperes"
And that's a typical figure for many cars. Current is even higher for large V8s. That's why there is no fuse in the starter circuit and the cables are such large diameter.
Note that the headlight fuses are 20A each, but the continuous current is more like 15A.
Finally, my suspicions about the omission in ETM manual on how high/low beam is controlled (by switching the ground lead on/off to the high beam bulb) has been confirmed. The schematic on Pg 23-174 of the shop manual is actually more detailed than the schematic in the ETM.
Last edited:
I had some issues with dash lights and headlights kinda working when they chose to in my '92 a while ago. Thread
I traced all of the issues back to a loose plug in the back of the dimmer control box on the dash.
-Remove the dash panel under the steering wheel and above the footwell to get access to that plug.
-Turn the car on and the lights on and wiggle that plug to see if it makes any difference.
If it does either the plug is loose, or the dimmer box or one of the associated control units may be faulty. The manual has trouble shooting proceedures that will cover everything except the plug being a little wonky.
I traced all of the issues back to a loose plug in the back of the dimmer control box on the dash.
-Remove the dash panel under the steering wheel and above the footwell to get access to that plug.
-Turn the car on and the lights on and wiggle that plug to see if it makes any difference.
If it does either the plug is loose, or the dimmer box or one of the associated control units may be faulty. The manual has trouble shooting proceedures that will cover everything except the plug being a little wonky.
Similar threads
