What could cause windshield wipers to come on while accelerating?

Dear Car Talk

Dear Car Talk | Jun 01, 1995

Dear Tom and Ray:

I have a 1988 GMC pickup with a V8 engine and automatic transmission. It is in excellent shape with approximately 85,000 miles on it. Recently, each time I step on the gas pedal a little extra hard for passing, the windshield wipers turn themselves on. Do you have any idea what would cause this?

TOM: We want to be perfectly clear about this right from the get go, Robert. We have absolutely no idea. But, of course, we won't let that stop us from speculating.

RAY: My guess is that something in the engine compartment is shifting when you accelerate hard. And that's somehow pushing against a wire and creating contact or interrupting a ground and somehow powering the wipers (notice the frequent use of "somehow" to mask lack of actual knowledge).

TOM: The problem is, it's going to be tough to find. If it's simply the torque (a.k.a. "twisting") of the engine that's causing this, you should be able to recreate the effect in the garage. Your mechanic can "load up" the engine by stepping on the brake and the gas at the same time with the transmission in gear. By the way, kids, the Society for the Prevention of Cruelty to Garage Doors suggests you don't try this at home.

RAY: If your mechanic can recreate the symptom in the garage like that, then you have a chance of finding the cause.

TOM: If not, then you'll have to try my method. I remove the hood, strap my brother to the engine compartment, and drive around 'til he figures it out...or threatens to tell mom.

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