Need help on my headlight issue.

[RandomGuy]

Hi guys. Yesterday when i warmed up the car i've noticed the right side headlight didn't light up. So i go out, got a new bulb and swapped it. But when i turn on the headlight this happens :



The one that i changed is dim. And when i turn on high beam i lost both high and low beam on the right side.



What i have done :

Swapped the bulb.
Check fuses : All good.
Check and clean batt neg terminal.
Check and clean the headlight "casing" connector.

Any other thing i can check/test before i send it to workshop? Car is 1991 RHD EUDM. Thanks.

 

[Honcho]

My guess would be a short in the headlight circuit. My 91 had a nearly broken wire on the passenger side headlight harness. I couldn't tell if the light going up and down caused it, but something similar might be happening on your car. I would examine the wires carefully and see if there is any damage.

 

[Miner]

An open in the ground perhaps. I suspect the service manual has a straightforward troubleshooting section for the headlights.

 

[Old Guy]

I am going to speculate that you have a damaged socket on the right headlight or damaged wiring in and around the right headlamp assembly. According to the service manual, there is a single relay supplying both the left and right headlights and a common ground for the left and right low beam and a separate common ground for the high beams which are switched through the dimmer relay. The fact that your left low beam comes on and the left high beam comes on says that the lighting relay, dimmer relay and the controls appear to be functioning as normal.

The fact that your right headlight initially operated poorly and then everything went dead on the right side after you changed the bulb reenforces the fact that it is a wiring problem in the vicinity of the headlight assembly. Unfortunately, the service manual only has a general schematic of the headlight wiring system and does not provide the physical details of the wiring. For the actual physical arrangement of the wiring (which tends to deviate from the simplified diagrams in the service manual - sometimes by a lot) you need the NSX Electrical Troubleshooting Manual. My copy of the manual is safely stored in the trunk of my car which is now locked up in winter storage so I can provide no details on the wiring arrangement. My advice is to start with the wiring at the right headlamp sockets (check the contacts in the sockets for damage) and then as @Honcho suggested, trace the wiring harness back from that point looking for damage. Since both the high beam and low beam on the right side are now dead I don't think it is the actual ground connection that is the problem since the high and low beams have separate ground connections. I would look for a problem on the red/yel wire which is the +12v supply to both the high and low beam.

All of this advice is based upon the LHD service manual so use with caution.

 

[Old Guy]

Courtesy of Heineken, here are grabs from the NSX ETS manual for the headlight wiring (on an LHD car).



As you can see from the diagram, if only the right headlight has failed and both the high and low beams have failed, it is likely the C282 6 pin connector or the wiring in the headlight shell itself that is the problem. It is also possible that the problem is in the wiring harness between connector C282 and C204 or between C204 and C246. However, the fact that the headlights went completely dead when you fiddled with the headlight bulb suggests the problem is localized to the headlight shell area. You should hope that is the case because finding a problem in the harness is much more difficult.

 

[RandomGuy]

Hi, thanks for the reply. Man i was hoping something that i can diy but looks like its heading to my workshop. Stupid question, i still haven't check the dimmer relay yet as i cant pull it out lol. Is there any clip that i need to release or i can just pull it out? Thanks.

 

[Old Guy]

Hi, thanks for the reply. Man i was hoping something that i can diy but looks like its heading to my workshop. Stupid question, i still haven't check the dimmer relay yet as i cant pull it out lol. Is there any clip that i need to release or i can just pull it out? Thanks.

The service manual shows no retaining clip for the dimmer relay. The picture of the relay looks like a conventional push to insert, pull to remove relay. It is a 5 pin relay so it will be more difficult to remove. They make special tools for the sole purpose of removing nasty relays

https://www.amazon.ca/Lisle-46950-Relay-Puller-Pliers/dp/B002NR2Z56

Given that your high beam functions correctly on the left hand headlight, the dimmer relay has to be functioning correctly. I would not bother removing it to check it - look elsewhere for the problem.

 

[RandomGuy]

I see. Thanks old guy. I'll update later if the issue fixed.

 

[RandomGuy]

Whoa, finally my reset password email arrived ( yeah forget the pass... ). Anyway fixed the headlights. OldGuy is right, apparently the main headlight socket near the the abs have a small burn. The socket is not tight enough somehow? I cleaned the small burned part and "clamp" the socket with zip-ties. Work well so far lol.

 

[Old Guy]

You might want to consider applying something like OXGARD (a conducting grease available from Home Depot) or Deoxit to the terminals in the socket to improve conductivity. The headlights draw about 5 amps of current per bulb and if the connection is poor (has resistance) it will heat up and create problems. That is likely what caused your problem in the first place.

 

[usafdarkhorse]

Reviving this thread since I just went through this on a 1990 Japanese market car, bright low beam on left side, very dim on right side.

I chased down the connectors from the wiring diagram above, but it turned out to be a blown right headlight fuse. Giveaway was that I had no high beam indicator light on the dash.

Hope this helps whoever happens to find this thread years down the road.

 

[Old Guy]

Reviving this thread since I just went through this on a 1990 Japanese market car, bright low beam on left side, very dim on right side.

I chased down the connectors from the wiring diagram above, but it turned out to be a blown right headlight fuse. Giveaway was that I had no high beam indicator light on the dash.

Hope this helps whoever happens to find this thread years down the road.

This is interesting because a completely blown fuse would not result in a dim headlight light. It should be completely out. It is possible that you might be getting a small amount of back feed through the dimmer light circuit. However, the bigger issue is that fuses typically do not just fail without provocation. You might want to take a close look at the wiring to make sure you don't have a wiring chaff that might be causing a temporary short to ground. Or are you using a non standard high wattage bulb which might require a larger fuse.