While the truck is running, the rear brake lights come on when i step all the way down on the brake. But when i turn the key over (truck not on) i can tap the brake and the rear brake lights come on.

Not sure what's going on, i replaced the brake light switch because i thought that was the issue.

Thank you.

 

It's normal for the brake lights to come on with the key off and/or with the key in the run position.

BB2

 

Yeah, but the problem is. That they only come on when i make a complete stop. I'm running the risk of someone rear ending because the lights aren't on as i'm slowing down.

 

So when your key is on the brake pedal needs to move further than when the key is off to actuate the brake light? That is strange indeed. Is your battery in good condition and your alternator is charging properly? How are the grounds in your truck? Check the grounds around the rear of the frame and for the ignition switch. Beyond that I'm stumped. Maybe somebody else has a clue?

BB2

 

I'm not clear what "turn the key over (truck not on)" means. Does that mean with the ignition switched off, i. e. key removed?

Does the following sound accurate?:

Engine running, the brake lights only illuminate when pushing the pedal way down.
Engine off, you only need to tap the pedal and the brakes lights work.


Not trying to bust your butt, just trying to make sure we correctly understand the symptoms.

Definitely a strange one, if I got it correct. Does your brake light switch have the funky arrangement where the switch moves with the pedal? That's how my '84 is. This flexes the wiring with each cycle of the pedal. On my truck, one of the wires eventually broke, but all that did was kill the brake lights completely. Not sure how a failure here could change the point when the lights illuminate, but check for a loose/frayed wire anyway.

Are you positive the variation is based on the physical location of the pedal? Or could the difference be how much pressure you are applying with your foot? Perhaps the power brakes change the equation. In other words, if you apply X amount of force with the engine off and thus no boost, the pedal only moves a small amount. Start the engine and now the power brakes are active. Apply the same X amount of force to the pedal and it moves further. Combine that with a funky wire flexing at the switch and maybe?

The only other thing that comes to mind is to compare battery voltage with the engine on and off. Maybe one condition is way out of specs.

 

Correct.


Correct, on the beginning of your post.

Yes, the brake light switch moves with the pedal. And i apply the same pressure when the truck is running or not.

I will check the voltage, in both situations and report back.

Thanks to both of you. I've been trying to figure this out for a couple of weeks. And i haven't been able to drive it because of the problem.

 

Any change of symptoms with the new brake light switch?

 

none whatsoever.

but it was weird that, as i had someone looking at the brake lights. While i was messing with the brake light switch, for a few seconds the brake lights stayed on. Not sure what i did. But then i moved the brake switch and it went back to giving me the same issue.

 

Here is an idea to help isolate a mechanical issue (switch actuation) from an electrical issue.

First test for the lights on when they shouldn’t be. Unplug the connector from the brake switch. Wiggle the harness around and see if the lights ever come on. Start the engine and repeat.

Next test for the lights staying off they should be on. Jumper across the connector with a paper clip or similar. The lights should come on. Wiggle the wiring, start the engine, etc. The lights should stay on steadily due to the jumper.

Try playing around with the turn signals and hazards. Power to the brake lights goes through both switches. Maybe something in there?

 

One difference between the truck running and not running is vacuum to the brake booster. You need some resistance in the brake pedal for the brake switch to work properly.

 

Alright, thank you gentlemen. I will do all that was recommended and report back.

And the brake booster was replaced, along with most of the brake system. I need to check and see all that was done.