I've been banging my head over this one, and it's been driving me crazy, every time I press the brakes the rear windshield wiper jumps, which is a real problem driving through town all the constant stopping. It's a 2000 Chevy Blazer LS, I've traced all my grounds and cleaned them, removed all the LED bulbs and went back to incandescent bulbs, I tried a suggestion from another thread and removed both brake lights, and the problem stopped. Hopefully someone can tell me where to go from here.

 

Try removing only one brake light then only the other and tell me if the problem stops or only when both bulbs are removed

George

 

Okay, so this morning I tried this...

Removed Left brake light - Rear wiper jumps
Removed Right brake light - Rear wiper jumps
Removed Both - Problem stopped.

After that, I reinstalled the bulbs and buttoned everything up. Checked the fuses just inside the driver side door and dash, just to make sure everything was seated good, and didn't find any issues,

Oddly enough, I then left to go to the store and the rear wiper isn't jumping when braking now, so the problem has become intermittent. While in town I drove a route that had speed bumps and several stops, trying to see if I could get the problem to replicate itself. Nothing happened, and the problem isn't there anymore.

I know this isn't a solution to the problem, because things just don't "fix" themselves. But for now it's gonna be hard to diagnose the issue if the problem isn't there.

I'm still stumped.

 

is there a simple explanation as to how the brake and wiper seem connected?

 

The brake light bulbs and the rear wiper motor ground path join at S427 (splice) and then goes on to ground G404 on the left rear body corner. Find that ground and clean it up and then follow the cable back towards that splice if you can get to it and look for damage or corrosion. you may need to cut back the black tape and reseal. If nothing then inspect the cable leaving the light assemblies since disturbing then changes the problem.

George

 

Normally the current path after the load is through a clean length of wire run to the chassis. When a load (light buld) loses its ground, it looks for another path to ground even if its a crappy one. If other components share that ground path at some point (S427) before the break or corrosion (S427-G404) then the signal goes through that load (wiper motor) and back down through some path to a different ground.

If thats not the problem then that ground wire (which is hot due to a failed ground) just after the brake light is shorted to the voltage feed for the motor in a shared cable run due to damage or corrosion. If the ground is ok then we chase this.

George

 

Either way, the problem is almost certainly mechanical damage or corrosion.

George

 

I was following the cable and seen the points where the wires where spliced, which seems to line up with what I see on the wiring schematic. Thanks for your help George, 2 heads are better than one. I'll get back with my findings when get back to it. I've got the holiday stuff going on, so it may be after.

 

no problem I’ll be here when you’re ready

George