Head light circuit issue

by 76 Malibu Thu May 21, 2020 7:12 am

There is a problem with the headlight circuit in my car. When I turn on the lights the high beam indicator is lights up even when I have the low beams on. The low beam headlights also seem to be at dimmer than usual. Activating the high beams, the indicator stays on, and the lights get much better.

My car was a stacked light car and now runs singles. I am using the original light harness for quad lights but left the high beams unplugged. I checked the grounds on the headlight circuit and they seem okay.

Anyone have any ideas on how to diagnose what is going on?

by 76 Malibu Fri May 22, 2020 12:46 pm

Anyone have any ideas? I am thinking it's a bad ground somewhere or maybe a bad light switch? I don't have any wiring diagrams for this car. Where are the grounds on these cars. I did also clean up the main battery ground.

by bigredlaguna Fri May 22, 2020 8:56 pm

So you have the high beam connector just loose up there? Did you tap into the high beam circuit to operate the high beams on the singles? Steve's Nova site has a lot of wiring diagrams that you can use to trace circuits. I know they are for a "Nova", but GM used the same color codes and routing across all lines with maybe a few exceptions.

Grounds may be the culprit here also. There are two on the core support near the headlights, and make sure the cowl to engine ground is secured. There is also a light circuit ground in the trunk. It should be near the latch.

by bigredlaguna Fri May 22, 2020 11:44 pm

I did a quick look for some schematics to see what the differences may be between a quad light and a dual light setup.

As far as I can tell, you shouldn't have any circuitry issues with leaving the high beam connectors unused. Outside of grounding issues, I would look at the dimmer switch. Perhaps the low beam side is faulty and causing a back feed into the high beam circuit resulting in the high beam indicator to light up.

by 76 Malibu Sat May 23, 2020 1:38 pm

Good idea on the high beam switch. Is there anyway to disconnect and bypass the switch so I can rule it out? I will check all the other the grounds. Where is the one that goes from the engine to the cowl usually located?

As for the headlights, I have just the high/low beam three terminal plug connected to my lights. The two terminal high beam plug is left loose. The headlights do switch from high to low beam but the low beams seem too dim. The high beams seem okay. So there definitely seems to be a problem in the low beam circuit.

by bigredlaguna Sat May 23, 2020 2:50 pm

The cowl to engine ground strap is near the centerline of the car behind the distributor. There are usually two branches that come off the cowl. One to the engine, and one to the hood.

There should be a connector to the dimmer switch that you can unplug and jump across terminals to do your checks. Just use a wire gauge at least the same size as what is going in/out of the connector in order to prevent creating a fusible link.

by 76 Malibu Sun May 24, 2020 3:12 pm

Thank you again. I will try bypassing the dimmer switch and checking the grounds again next time I have time to work on the car.

by 77camino Tue May 26, 2020 2:00 pm

Was curious if you still had the original quad setup. Of course you do, we never get rid of anything for our cars. Lol! Have you tried to plug the 4 original headlights back into the harness and see if things work properly. I don’t think the harness would be long enough to reach without removing the whole assembly. Maybe you could make an extension harness and Just lay the headlights on the core support.

by 76 Malibu Tue May 26, 2020 6:04 pm

Yes I do, I never throw anything out! Very Happy

They are stored away, but I could dig them out for a test. Thanks for the tip.

by Zed06 Sun May 31, 2020 10:49 pm

I've seen this before, but from the opposite direction. I updated the headlamps in two of my 75 Caminos from singles to stacked. You have the sealed beams wired wrong. The connections on the square lamps are not the same terminal pattern. Take a single round lamp and mock it up on the bench. When you identify which terminal does what, go to the wiring diagram and change the terminal locations in the connector to the lamp accordingly.

by 76 Malibu Tue Jun 02, 2020 6:37 am

Zed06 wrote:I've seen this before, but from the opposite direction. I updated the headlamps in two of my 75 Caminos from singles to stacked. You have the sealed beams wired wrong. The connections on the square lamps are not the same terminal pattern. Take a single round lamp and mock it up on the bench. When you identify which terminal does what, go to the wiring diagram and change the terminal locations in the connector to the lamp accordingly.

Thank you!! This was the problem. I had no idea that the rectangular lights terminals were different from the rounds. I found this article ere which shows the terminal layouts for the different bulbs.

http://www.experts.com/content/articles/Mike-York-High-Low-Beam-Filament.pdf

I change the terminals around in the connector and now the lights are brighter and the high beam indicator only lights up when the high beams are on. Thank you again.

by bigredlaguna Tue Jun 02, 2020 9:33 am

I never would have thought about that by just looking at the diagram. Thank you.

by 77camino Tue Jun 02, 2020 9:57 am

Wow! Who would thought that would the case. Don’t ever see myself changing mine, I prefer the quad lights, but it is good info to know. Glad it worked out for you!

by Zed06 Tue Jun 02, 2020 2:48 pm

Glad I could help.

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