I've had 3 >=1989 cars this year that had a starter with a solenoid that would click but not engage the starter motor.

In each case I first cleaned the battery-ground connection to the block, battery lead to starter, and both battery-post connectors. No difference - none worked.

Also, in each case, the starter worked on the bench - engaged easily - but not when put back in the car.

1. A stick-shift a friend bought after it sat in a garage 2-3 years. The starter failed for the PO; he replaced it with a cheap reman unit; got a faint click and then nothing; gave up. After the starter worked on the bench but not back in the car for me, I removed and examined again. There was a thick layer of black paint on the starter flange (where it bolts to the engine) and rust/paint on the block. I cleaned both faces, roughed up the starter flange with a file, installed and it started right up. No problems in ~ 6 months since the repair.

2, 3: Both cars been sitting a few months. Removed starters, found that each worked fine on the bench; cleaned & replaced in the car; still just a solenoid click. Tried a different starter in each car and it worked no problem.

This Winter I'll check these two starters for amperage draw. But I suspect a ground problem.
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240 drivers / parts cars - JH, Ohio