running lights come on while braking

[jonb96150]

I'm wondering if someone had this happen and can point out some likely places to check.

1987 bj-70 24 volts. When I apply the brakes the running lights come on including the dash lights. The dash lights are about 1/2 the brightness when pressing the brake pedal than when the running lights are turned on with the switch.

It would seem that the brake light circuit is energizing the running light circuit. I'll start by pulling the taillights and checking for shorts and working from there.

TIA for any advice.

 

[FJ40_owner]

I'm wondering if someone had this happen and can point out some likely places to check.

1987 bj-70 24 volts. When I apply the brakes the running lights come on including the dash lights. The dash lights are about 1/2 the brightness when pressing the brake pedal than when the running lights are turned on with the switch.

It would seem that the brake light circuit is energizing the running light circuit. I'll start by pulling the taillights and checking for shorts and working from there.

TIA for any advice.

You are not looking for a short but a cross. Somewhere you are feeding back voltage from the brake circuits to the run lights. I suggest you look for areas where the wires might run together and look for frayed, torn or corroded connections that have some form of common connectivity.

Good luck.

JB

 

[Jim_Hbar]

Bad grounds can cause all sorts of wonderful symptoms, with the current back-feeding through other circuits. Happens just about every time I hook up my trailer

And the biggest identifier of this problem is the lights are dimmer when they back-feed, just like you mention. I'd give it about an 80 to 90 % probability that it's a grounding problem at or around your tail lights.

Jim

 

[jonb96150]

Thanks for the replies!
No evidence of cross connecting at the tail-lights, and the common ground wire shows no voltage.

 

[jonb96150]

The gremlins disappeared during a lull in the action. Must have sensed my absence and made their escape. I have no idea why or how, but it's all good now.