TR2/3/3A TR3 Right Brake Light Issue

[CCURTISS]

Without the running lights on both brake lights work when I apply the brakes.

Now here is the strange part, when the head lights are on and the brake is applied the left light and brake light work fine but the right light goes totally dark.

Both the brake light and the running light seem to be a little dimmer on the right. I have switched the bulbs and the right light still has the issue.

Any ideas?

 

[DNK]

If 1 side is dimmer than the other I think that usually means grounds.

 

[TR3driver]

Now here is the strange part, when the head lights are on and the brake is applied the left light and brake light work fine but the right light goes totally dark.

Classic symptom of a bad ground.
When either set of lights are on, the right lamp grounds through the other system's other bulb(s) (which also explains why it's a bit dimmer). But with both sets on, there is no current path through either right filament, so the right bulb goes out.

The original ground is through the 2 screws that hold the fixture, and the clip nuts that the screws go into. Usual problem is corrosion (or paint if recently painted) between the clips and the body, but of course could be anywhere along the path.

My suggestion is to add a ground wire to all of the rear lamps. They have sockets for bullet connectors already, so all you have to do is make up the wire(s). Mine daisy-chains across the back, then runs forward to one of the gas tank bolts. Chances are, the other lights will get brighter as well.

 

[CCURTISS]

Perfect, it turned out the clips on the trunk side for the mounting screws were rusted and loose. I replaced the clips and it all works now.

Thanks!

 

[Geo Hahn]

Bad grounds produce some truly squirrely results. I had a bad ground on one headlamp that caused the headlamp not to work and the high beam indicator to be on whether hi beams or low beams were selected.

 

[DrEntropy]

Electrons are an opportunistic lot. Path of least resistance every time. Whether that means goin' thru the high-beam indicator lamp, or the filament of the left rear running light. Squirrely, indeed.