Strange tail lights lights behavior

[Showdown]

Hey friends...

Anyone ever seen anything like this:

Running H4s with city lights. I just wired up my R-style lights. I have a combo turn signal/reverse light housing and a combo running lights/brake light housing. 4 bulbs per side.

I wired them up according to the tail lights I removed and the flow chart for my car: a 1977 S US delivery

Everything works exactly as it should as long as the running lights or headlights are OFF. If I turn the running lights on or headlights on, everything is all haywire.

Video below:

First pass is with no headlights or running lights on: left turn signal, right turn signal, brake, reverse: everything is copacetic.

Second pass is with running lights on: left turn signal, right turn signal, brake, reverse: everything is haywire.

Third pass is with headlights lights on: left turn signal, right turn signal, brake, reverse: everything is haywire.



No fuses are blown, the headlights and city lights work as they should, no LEDs no LED relay.

Totally stumped as to why the circuits would change when the headlights or city lights come on. Other than this, I haven't done a thing to any of the lighting wiring or circuits.

[Showdown]

You know, I don't claim to be an expert in anything Porsche but I think of myself as pretty clever and capable at times.

This car will undermine that no matter what.

First rule of Porsche; it's the grounds. It's always the grounds.

Even after testing my grounds and getting satisfactory readings I decided to run a new ground wire to the engine case and low and behold... the problem disappeared. Damn grounds.

So now the question is where to ground the lights... to the tub with a hole and screw or into the engine bay to a ground post... hmmm.

Thanks for playing "Julian's an idiot" back to your regular scheduled forum browsing.

[PeteKz]

Sometimes just saying it out loud helps you focus on the problem. Glad we could help!

[chrisbalich]

Hey, Julian.
Check the grounds.

<3
CB

[Showdown]

Thanks Chris, you trying to get your post count up?

[chrisbalich]

Originally Posted by Showdown

Thanks Chris, you trying to get your post count up?