No high or low headlights

[Wackjum]

Hello. Currently my high and low beam headlights only work randomly. Here are the observations and things I have tried:

• If I turn the headlight switch, both housings pop up, but the lights don't come on.
• If I pull back on the high-beam stalk, both housings come up but the lights don't come on. I do not get any indicator on the dash that my hi-beams are on.
• I tested the lighting relay. It passed the test but I changed it anyway with no different results.
• I tested the dimmer relay. It also passed the test, but I have not replaced it.
• My dimmer switch in the cabin appears to do nothing. I have unplugged and replugged and wiggled the wires going into that area as well. I have lighting in the instruments. I just can't change their brightness.
• I've tested and swapped and changed both side's fuses.
• I have not changed the bulbs since they do work sometimes. But I have swapped them left and right.
• I said that the headlights work randomly. When they work, everything works (both high beams and both low beams) I cannot detect a pattern of when they work. Usually they do not work. Since the headlights are unreliable, I do not drive the car at night. But what happens is when I get in the car, I wonder if they might work this time and do a quick test. Even if I just leave the car alone and come back later with the only difference being turning it on and off, the lights may or may not work.

My guess is a bad/intermittent common ground. for the headlight circuit. But any advice or where to start would be appreciated. I can't get my car to pass my state inspection so my car's registration is 3 years out of date.

 

[Old Guy]

This is the headlight circuit which is separate from; but, connected to the headlight door circuit. As a result, the headlight doors can operate just fine with dead headlights. The headlight circuit is fairly straightforward, unlike the headlight door circuit which is definitely not straightforward. Be happy that the doors work!




A flaky ground G403 will stop the low beams from operating; but, not the high beams. A flaky ground G201 will stop the high beams from working; but, not the low beams. As a result, it seems unlikely that either of those grounds is the problem. Ground G401 is the ground associated with the light bulb control function and it can kill everything. Check G401 which is the black wire coming out of the lighting switch.

You said you tested 'both sides' fuses. That is confusing because there is only one fuse for both sides. There are separate low and high beam fuses #52 and #49 if that is what you meant. If not, check those two fuses.

If the G401 is good, then I think you need to do a function test on the lighting switch. The low beams and high beams get powered through the lighting relay which is directly controlled by the lighting switch. When the lighting relay is energized the low beam always come on The high beams get switched on by means of a separate ground path controlled by the dimmer relay. Given that you have random operation of the headlights, if G401 is good then I bet that you have an intermittent or dirty contact in the headlight switch that controls the headlight relay.

Page 23-177 of the service manual contains a pin out diagram of the connector for the lighting switch and a switch terminal connectivity table which will allow you to confirm the operation of the switch. Note the diode indication in the connectivity table. In order to check the switch operation you must have the - lead of the tester connected to the cathode side of the diode (in most case terminal 1 - the black wire). Do it backwards and the switch will always show open circuit. You can get a copy of the service manual from the NSX Prime Library

Factory Service Manuals

As our NSX continues to age, it will become more and more important for member to be able to service their cars. Most Acura dealers no longer employ technicians who are familiar with the NSX, as the original techs are long gone or retired. As...

www.nsxprime.com

Edit
Just for clarity, I should have included this diagram which is 'mostly' the retractor control circuit. What is relevant is the little area shown circled in red which is part of the headlight switch.



What is significant is that the headlight switch knob actually controls 4 separate sets of switch contacts. Two switches control the light bulb and tail light operation and two switches control the retractor operation. The part of the switch that controls the headlight relay circuit can fail and still leave the tail light and retractor doors functioning fine.

You did not say anything about tail light operation. Do they work OK?

 

[Wackjum]

Thanks for your very very detailed reply and diagrams. I did not get a notification my post was approved so I had not checked back. I'm still dealing with the problem, although I just purchased and received my "Power probe" so hopefully this weekend will be fruitful.

These are the two fuses I checked that I thought was for the headlights.

 

[Old Guy]

My apologies. It is left and right, not high and low as I wrote and those are the correct fuses to check. I am not sure where my head was at when I wrote that comment, perhaps the morning shot of caffeine had not completely taken effect.

 

[Wackjum]

My apologies. It is left and right, not high and low as I wrote and those are the correct fuses to check. I am not sure where my head was at when I wrote that comment, perhaps the morning shot of caffeine had not completely taken effect.

I fixed my headlights this morning! It was the headlight switch.

Your post was key as you said the pop up mechanism and lighting were two separate circuits. I had assumed they were the same so I did not focus on the switch since I thought it was sending power.

Took apart the steering column, cleaned the contacts for the headlight switch, re-assembled and everything is working. But in the process I noticed my cruise control and headlight wedge bulbs are all out. So going to keep the dash apart while I order those things.

It's always something on these old cars...

Thanks again.

 

[Honcho]

It's always something on these old cars...

Ain't that the truth!

 

[Old Guy]

It is good that a clean-up did the trick because the headlight switch is part of the combination switch assembly. In North America it is only available if you purchase the complete switch and combination assembly which has a discounted price of a nudge under $1500 US$. Just the headlight switch part might be available from Amayama for a much more reasonable price if you can sort through the part number discrepancy. I don't think there is a difference between RHD and LHD; but, surprises abound.

A couple drops of DeOxit D100L on electrical contacts can work miracles.

 

[Heineken]

I fixed my headlights this morning! It was the headlight switch.

Your post was key as you said the pop up mechanism and lighting were two separate circuits. I had assumed they were the same so I did not focus on the switch since I thought it was sending power.

Took apart the steering column, cleaned the contacts for the headlight switch, re-assembled and everything is working. But in the process I noticed my cruise control and headlight wedge bulbs are all out. So going to keep the dash apart while I order those things.

It's always something on these old cars...

Thanks again.

Sorry for jumping in - wrote a lengthy article on bulb replacement at the cluster, including types, wattage, etc. - might be of interest to you: http://www.nsxcb.co.uk/entry.php?2732-Gauge-Cluster-Bulb-Replacement