I was checking the bulbs and sockets of my Satellite lights today and had my son try the reverse lights, brakes, running lights, etc while I watched what worked or what didn't...

One thing was really weird - I had the lenses off for cleaning so I could for the first time watch what the individual BULBS were doing up close..

Applying the brakes, the filament of the Running lights and the Reverse lights also came on - but just glowing slightly - as if some voltage was "leaking" to the other filament.. so I looked for the same thing in other conditions.

- In Reverse, the brake and running light bulb also glows dimly, as if voltage is "leaking"..
- Turning the Running or Headlights on and everything looks normal, no other bulbs glow..
- Brake lights, like I said above, they "leak" voltage to the other Running light and Reverse light bulbs..
- The brightness on the other bulbs would increase if I pulled one of the dimly glowing bulbs, so that's a "load" on the circuit.. obviously.

How do I start troubleshooting this to find the "leak"? Or is this somehow normal?
I stink at electrical issues, but I usually succeed with help.

The wiring all looks decent enough, but could there be worn insulation in the wire loom and a small amount the power is crossing over from one wire to the others?

The fuses were all cool to the touch.
The FSM doesn't mention it.
The Wiring diagram doesn't reveal much.
The wiring connectors to the Light, Reverse and Brake switches looked good.
Each switch made good continuity.

Thanks,
- Art

Everytime this has been a bad ground at least for me. Do you have a FSM for the wiring diagram? This can get tedious but if you isolate each harness, starting at the rear, use a 12v power supply to check each bulb circuit, usually finds the problem(s).
Good Luck

As A990 said possible poor ground connection, connect a temporary ground @ each lamp assy.& see if this corrects the issue.

I’d bet 2 dozen larryLOVEit donuts ....

It’s a bad ground. I went through this just recently with a 24 foot enclosed trailer

Another vote for poor ground.

I went through and replaced my tail light sockets with the ones that have the tab on it for a ground.
Due to paint and spray on crap in the trunk a lot of lights in my 65 didn't work right. So instead of chipping away at the whatever it was I just did that instead of trying to mess with tracking down what grounded and what didn't through the housing.

Thanks guys,

YOU ARE ALL CORRECT!!

I put on my Big Boy pants and a headlamp and went to work on it early this morning.
I used jumper wires, a continuity device and volt meter to trace how far the +12V power was getting, all the way around to the ground..
Then used the continuity device to isolate the problem to a Ground wire screwed to the sheetmetal - there wasn't continuity across the connection.
Wire brushed it clean, gooped a little anti-corrosion lotion on it and the problem vanished.

That solved one side, and I found the other side was the exact same thing.

Cheers,
- Art

Good to hear!
I had a Dart years ago that had painted over grounds and a shredded ground wire. Plus a fried wire in the underdash harness caused by an assembly error. caused a lot of till I chased it all down

I've run into ground issues with lighting so much, I've reached a point where I ground every light housing. I really like the replacement light sockets with the ground tab.

I now will clean a place at the front, the rear, and at the bottom of the dash that I make ground points. I'll find a pinch weld ares that is pretty easily accessible, then I remove the paint down to shiny metal, then I will drill a 1/4" hole and add a 1" long bolt with a nut and flat washers if there is room. I stick the bolt through the hole and run the nut up tight against the metal. Then I add a 1/4" eyelet to each ground wires for every light, or anything else that needs a good ground. Those eyelets go against the tightened nut, then I add another nut and tighten it down. Presto, a very good ground that lasts at least 5 years, you can even use it as a ground to test stuff. When the bolt becomes degraded, or has an issue, I will simply replace the 1/4" bolt, clean up the mounting surface again, and change the eyelets if needed, with another all new setup. Its cheap, easy, and works very well. Gene

On your jumper to check the ground stick a thin pin to make contact with the actual bulb metal case

I teach some automotive stuff...one of our sayings is " grounds,grounds,grounds!!"