Driver side brake light gremlin

[qualityhardware]

My driver side brake light is operating inconsistently. Whether or not I have the lights on, it will not illuminate when I step on the brake pedal. If I run the left turn signal, it flashes without a problem, and then the driver side brake light will work as it should.

Pulled the whole tail lamp assembly. Checked the bulbs - all good. Checked the connections - all good. Cleaned all of the connections. Checked the brake light switch connections and cleaned them. Checked the connection of the rear service light harness to the main harness. Good. Cleaned the connections. Basically, I walked the harness from the tail lamp assembly to the dash / fuse panel as per diagrams F-13 and F-14 in TM9-2320-289-20 and checked everything, and so far, so good.

I'm stumped as to what's failing here. Any ideas? I am having zero problems with the passenger side brake light.

 

[MarcusOReallyus]

I'm thinking there's a high resistance you haven't found, or a bad ground. Did you look at the grounds?

 

[steelandcanvas]

Sounds as though the problem could be in the turn signal switch. Even though your left turn light flashes, in the neutral position (center, no turn) the brake lights are still routed through the turn signal switch. A disassembly and cleaning may be in order.

 

[c hawk19]

I'm thinking there's a high resistance you haven't found, or a bad ground. Did you look at the grounds?

Though I am no expert it sounds like a bad ground to me also.

 

[qualityhardware]

I'm thinking there's a high resistance you haven't found, or a bad ground. Did you look at the grounds?

Grounds are good to go. Checked and double checked with a meter and everything. That's part of the frustration.

 

[qualityhardware]

Sounds as though the problem could be in the turn signal switch. Even though your left turn light flashes, in the neutral position (center, no turn) the brake lights are still routed through the turn signal switch. A disassembly and cleaning may be in order.

Will give this a shot. Thanks for the guidance.

 

[steelandcanvas]

Will give this a shot. Thanks for the guidance.

My pleasure. I think you'll be on the right track after all your troubleshooting, to look at the turn signal switch as the culprit. If it was a grounding problem, the lamp wouldn't light, the turn signal function and brake light function share the same filament in the lamp. The flashing turn signal proves the ground path is OK.

 

[MarcusOReallyus]

Not necessarily. Partial grounds can do wondrous things. Hair pulling wondrous things.


But I agree the switch is the next most likely culprit. But you can't just rule out grounds because a circuit works some of the time.

 

[steelandcanvas]

Not necessarily. Partial grounds can do wondrous things. Hair pulling wondrous things.But I agree the switch is the next most likely culprit. But you can't just rule out grounds because a circuit works some of the time.

I agree with you also about the grounds creating havoc, but my gut says "turn signal switch". He did mention he checked everything with a meter.

 

[MarcusOReallyus]

I agree!

Just posting the clarification for the benefit of folks who might read this and not understand what really, REALLY weird symptoms bad grounds can create. Especially partial grounds.

Grounds should be checked with a really good low-resistance lead going to a solid connection at the battery ground terminal itself.