Cage brake Lights

[Bob_Roller]

I've noticed over the years, cars that would have one brake light bulb stuck in the brake 'ON' mode, while the other brake lights operate normally .

I've looked at the wiring diagrams to the cages I have, and other than someone messing with the wiring, I can't see how this happens .

Any other idea out there ?

[Rob Valdez 79 R65]

I once posed a similar question on Boxerworks, about the wacky way some vehicles lights would work when the brake pedal was applied.

I believe it was Robin Frankham that replied that is generally caused by a ground fault, (an open) and the electricity, looking for the path of least resistance, goes through a lamp filament, possibly backwards???

All I know for sure, is I'm not at smart about electrics as Robin, and I think this was pre-meltdown of last summer's database.

[nhmaf]

This seems to happen alot on Volvos - even the newer ones, I think.
Rob's statement is correct, to my knowledge - at least some of these vehicles share a common wiring scheme where the left directional wiring shares a common wire with the brake light wiring.  IF the directional is not on and the brake light circuit's path is interrupted it can find a path through this other wire back through the flasher relay connection.   At least this was the case with some older vehicles.   I think the reason it happens more on Volvos is that many of these cars have a "fog" mode that engages another circuit/bulb for brighter tailights in low visibility conditions - this provides yet another wire path for completing an otherwise broken circuit.

[Bob_Roller]

That makes sense, I had an'81 Mercury LN7 cage, similar to the Ford EXP .

It developed an interesting electrical anomaly, on rare occasion, when you turned the headlights on, the left headlight would be dim, the left turn directional would stay on, the windshield washer fluid low warning would come on, and the windshield wipers would come on to the slow setting .

Culprit, an extremely rusted ground connection .

If it hadn't been for the electrical section in the maintenance manual, I don't know if I ever would have found that particular ground .

[nhmaf]

Gee Bob -

That sounded like you needed an exorcist instead of some electrical work!

[Bob_Roller]

It was a bit odd, to say the least bit !!!!