1990 240 wagon pressing brake turns off rear running light

[edelmatt]

When I've got the running lights on (middle switch position), pressing the brakes turns off the left rear running light (bottom combo bulb) and the left rear brake light doesn't come on. When the headlamps are on (right switch position) or fully off, the left rear brake light functions normally.

I've already inspected the bulb and holder and all seems fine. I'll go and double check with the hopes that the problem is with the lamp or holder. But if anyone thinks it may be something else please let me know. Hopefully not somehow the bulb out indicator. I've had that apart already today trying to track down another issue, and it 'looks' fine.

Thanks for any help!

UPDATE: I tested the resistance between the bulb holder leads and the conductive strips on the lens assembly. Noted there was about 15 ohms of resistance for the brake lamp lead. I didn't work it all out, but apparently with the running light on, putting voltage across the brake lamp grounds out the running lamp. I jammed an eye connector between the holder lead and lens assembly conductor, and that makes a zero-resistance connection. SOLVED.

[abscate]

Classic bad ground/connection problem - if you trailer anything you get used to seeing this problem.

[jimmy57]

Depress brake pedal with a stick or whatever and then go back and shift the bulb socket to see if it remedies itself. The bulb sockets on these often gives this problem. Sometimes it is tail light housing melted enough that bulb socket is not being held against the conductive strips on tail light back side.
The ground contact is the one that gives the issues.

[edelmatt]

Thanks guys. As noted in the first post, I found there was resistance where the brake bulb lead met the lens assembly conductor. The conductor was more or less worn through at the point of contact. So for now I put a wire connector lead between the two parts to get a low resistance connection.