Brake light on dash

[FJCthulhu]

Hey look it's another "why is my brake light on" question, or questions...

1992 HDJ81
Brake light on dash wants to get noticed. All the time every time.

Ruled out parking brake switch, it's fine.
Ruled out the brake reservoir fluid level sensor, and left it unplugged "for now"

Are there any other trees to bark up?
Fuses? Thoughts? Prayers? Magic?
Is this going to be a dash disassembly / checking for wiring issues adventure?

Any advice appreciated, even if it's a bad story.

 

[jonheld]

The only things that illuminate the dash brake lamp are the hand brake switch and the float in the reservoir cap. If you unplugged the reservoir cap and the light went off, then you know what the answer is.

 

[FJCthulhu]

The only things that illuminate the dash brake lamp are the hand brake switch and the float in the reservoir cap. If you unplugged the reservoir cap and the light went off, then you know what the answer is.

Hey Jon! Hope all is well.
Yeah, that sensor is currently unplugged.
Parking brake switch is good.

Light is still on.

Next stop is the brake vacuum reservoir, I think.

EDIT: I just learned the diesels have a vacuum reservoir tank on the LH side of the engine bay. I guess the gassers get that vacuum from somewhere else. So I'm checking that tank & the rubber hoses going in & out of it for leaks next.

 

[Malleus]

Hey Jon! Hope all is well.
Yeah, that sensor is currently unplugged.
Parking brake switch is good.

Light is still on.

Next stop is the brake vacuum reservoir, I think.

EDIT: I just learned the diesels have a vacuum reservoir tank on the LH side of the engine bay. I guess the gassers get that vacuum from somewhere else. So I'm checking that tank & the rubber hoses going in & out of it for leaks next.

Gasoline engines produce vacuum (low pressure) to move air/fuel, diesels don't. That's why diesel engines have vacuum pumps.

 

[FJCthulhu]

Gasoline engines produce vacuum (low pressure) to move air/fuel, diesels don't. That's why diesel engines have vacuum pumps.

Thanks! I'm learning about this as I go and appreciate the notes. I'm hoping this is just the sensor on the tank.