Rear tail light problem, or haunted car?

[Cveezy]

Hello, I have an e24 1985 635csi. My rear passenger tail light is not working. The rear driver's side works 100%. I'll be separating info to make it easier to explain, as well as troubleshooting done.

What works
Reverse light
Brake light
Turn signal

What Doesnt work
Rear tail light (light that glows so people know you are there ill call it "idle light")

Vin= Voltage in

1)The first thing I did was swap bulbs, left to right and right to left. The known "good" bulb did not work on the passenger while the "bad" bulb worked on the drivers. So the bulb is not the problem.
2)The socket was cleaned to make sure it was not a contact problem. It did not resolve the issue.
3)Problem should not be the fuse as the driver's side works and every other light in the tail light works.
4)Took a multimeter and checked at the socket voltage.. was 0
5)Removed "wiring harness" from back of light, checked voltage at idle light Vin and ground directly at harness. was 12V (great this means the problem is the socket.) Wrong
6)With loose wires attached light bulb to the harness...no light. While still attached to bulb I checked with multi meter, and had full 12v...(WTF!?)
7)Took wire out of "idle light" Vin and attached to turn signal and it works (I had the signal blinking for testing purposes)
I then ran a Vin line from the plate light to test the ground wire and there was no problem.

I'm lost. The car clearly defies laws of science in my step 4,5,6. Anyone have some helpful insight,hints,prayers,voodoo?

[ron]

This post needs moving to "Engine- Mechanical- Electrical" but unable to do so as no "Moderator" function in "Workshop".

Brian??

[Cveezy]

This post needs moving to "Engine- Mechanical- Electrical" but unable to do so as no "Moderator" function in "Workshop".

Brian??

Ahhh, i was wondering where exactly to put. I only saw engine mechanical, too much skim reading =x.

[sharkfan]

I would say there are dodgy corroded contacts, not enough 'spring' in the bulb base contact and possibly an iffy wire.

You're doing exactly the right thing by progressing methodically but check you're getting good contacts/circuit continuity where the loom plugs into the rear light cluster and where the bulb touches the contacts.

[GRNSHRK]

And while I recall you mentioning that you couldn't move posts in the "Workshop" section, I'm able to

Anyhoo, she's in the correct forum now

[Cveezy]

I would say there are dodgy corroded contacts, not enough 'spring' in the bulb base contact and possibly an iffy wire.

You're doing exactly the right thing by progressing methodically but check you're getting good contacts/circuit continuity where the loom plugs into the rear light cluster and where the bulb touches the contacts.

I thought cluster check should have confirmed the voltage problem, maybe ill remove the power for the idle light out of the cluster and directly connect it as a test.

[Pod]

Bad earth

[Cveezy]

Turns out the problem was a loose connection in the rear relay! Its all good now.