Starter problem - need help
 

I am having a starting issue that is driving me bonkers. (84 3.2) I started my car and drove it 20 mins, shut it off, 20 mins later I go to start it and it does not turn over. The Solenoid clicks but the motor does not spin. I put the jump pack on it, no change. I assume that the starter has gone out so I replace it. I go to start it and I get the exact same symptom! I spent all day checking wiring and connections, I have power at the main starter terminal, I get power on the yellow lead wire everytime that I turn the key. I have tested the resistance in the main battery lead all the way to the starter and it is good. I have tested battery and engine ground straps. Occasionally I turn the key and it fires right up, maybe 1 out of 10 tries and I don't have to wiggle any wires or do anything between trying, most of the time just "click." Oh I also put the battery on a slow charge overnight and then tried a different battery - "click." So I think I must have gotten a defective new starter. I pull it out and replace it with another Bosch reman unit. Same problem! They all seem to bench test fine. What could be wrong?! The starter motor and the solenoid share the same power source and the same signal from the ignition switch, why does the solenoid always work and the starter motor (almost) never work? Thanks for any help!

Update - I *think* it was the positive battery cable all along. I made a change in how it was tightened down which in turn straightend out the wire a bit and I cleaned up the connection with PB blaster. I guess it had a good enough connection to send 12 volts and light up my test light, and enough to show no resistance but not enough to carry all of the current needed to turn the motor. What a pain.

For the age, I would look at the ignition module on the back of the key. Your main power is direct from the battery, the yellow wire comes through the ignition key.
Try jumping the starter at the starter, you should start,
Bruce

thats what i was going to suggest because you sadi you tested the connections instead of clean them.

like you said, the connection can be good enough to measure 12v, but not good enough carry the current needed for the starter.

a multimeter can really make this show up for low current circuits, but with the starting circuit, it is just better to just clean EVERYTHING.