Tail light and dash light problems

[Liffa]

I have been trying to trouble shoot some electrical problems but I cant figure out what is wrong. The car is a 1983 e30 coupe. I have not installed any front headlights yet, but something is going on in the rear.

When the light switch is in position 0, fully pressed in, no lights are on. This I understand is correct.
When the light switch is in position 1, parking mode, left and right taillights come on, the dashlight/cluster illumination comes on and can be dimmed.
When the light switch is in position 2, ON position, only my left tail light works and the dashlight turns off.

What could be going on here? Do I have a short somewhere? I dont get 12V out from the switch to my left tail light in position 2 (pin 1 of the light switch connector) I have tried another light switch with the same outcome.

Brake lights and number plate illumination works as it should btw.

[tomstin]

You need to get a wiring diagram for your year. On my 85 the wiring diagrams show a "rear lights check relay" that appears to only affect the tail lights and not the side markers?????

[Edrift]

I have been trying to trouble shoot some electrical problems but I cant figure out what is wrong. The car is a 1983 e30 coupe. I have not installed any front headlights yet, but something is going on in the rear.

When the light switch is in position 0, fully pressed in, no lights are on. This I understand is correct.
When the light switch is in position 1, parking mode, left and right taillights come on, the dashlight/cluster illumination comes on and can be dimmed.
When the light switch is in position 2, ON position, only my left tail light works and the dashlight turns off.

What could be going on here? Do I have a short somewhere? I dont get 12V out from the switch to my left tail light in position 2 (pin 1 of the light switch connector) I have tried another light switch with the same outcome.

Brake lights and number plate illumination works as it should btw.

This doesn’t really sound like the light switch since you’ve already tried another one with the same result.

On E30s, this kind of weird behavior is usually a bad ground or issue in the rear light wiring. A poor ground in the trunk can cause backfeeding, which gives you one side working, odd tail light behavior, and even dash lighting issues.

I’d start by checking/cleaning the rear light grounds and inspecting the trunk loom for broken or corroded wires before chasing anything else.

[Liffa]

This doesn’t really sound like the light switch since you’ve already tried another one with the same result.

On E30s, this kind of weird behavior is usually a bad ground or issue in the rear light wiring. A poor ground in the trunk can cause backfeeding, which gives you one side working, odd tail light behavior, and even dash lighting issues.

I’d start by checking/cleaning the rear light grounds and inspecting the trunk loom for broken or corroded wires before chasing anything else.

Ok, thanks! I have now tried three different switches and the problem is still there. The ground for the rear lights should be located under left side of the rear seat? This ground I have checked and cleaned before. I thought since the lights work in parking mode it is probably not a ground issue, but it is almost always a ground issue I guess 😆

I figured out that the problem affects all lights correlated to fuse 23 only. Also the license plate illumination go black in position 2.

I started up the car the other day (after 12 months lf restoration). After 15 minutes of idling these problem lights suddenly came on. However, after moving the switch to position 1 and back to position 2 the lights went out again. So maybe heat/vibrations made a bad ground abit better?