Any explantion for how a “bad” starter motor can crank the engine, but use too many amps in the selenoid circuit?
I had this problem when I installed a rebuilt starter motor in an early 1990’s Toyota Corolla recently. It was one of those offshore rebuild starter motors. When I installed it, and turned the key to start, nothing. ARRG … I have to take it back, and it takes me about 2 hours to install it, and another 1 hour to remove it! It’s not like changing a lightbulb!
Anyway, first off, before removing it, I checked the voltage (that comes in the smaller cable from the ignition switch,not the one in the thick cable direct from the battery) right at the starter selenoid, and it was only 8.6 volts. At first I thought it was a weak battery, but the battery voltage was 11.8 volts under the same load at the battery. And the voltage at the ignition switch was 11.6 volts. It was loosing 3 volts in the wiring path from the ignition switch to the starter motor! Then I noticed the wiring harness was getting warm that held that wire. Oh Oh.
For the life of me I couldn’t figure out what was wrong. Unwilling to throw in the towel and remove the unit, I decided to completely bypass the ignition switch and the entire wiring harness, so I wired it up with my own switch I bough at Radio Shack and my own 16 AWG (the wire in the harness is 18 AWG) wires clipped direct from the battery to the starter selenoid. This is all from the front of the car. I just wanted to see if I could get it to turn and crank the engine. It worked, it cranked ok and everything, but the second time I tested it with this experimental configuration, it melted my 10 Amp Radio Shack switch! The switch was supposed to be able to handle 10 amps! Remember, this is the selenoid circuit, not the main power circuit from the battery.
So I then DID throw in the towel, and took it out, took the starter motor back to the auto parts place. ( I had a little dust-up with the parts place manager; he at first refused to refund my money. He wanted me to take another rebuilt one, but I’d lost trust in their rebuilt units and I just wanted my $$ back. We compromised on a voucher for future purchases.) Anyway, the parts place tested the problem starter motor I had returned to them, and they said it tested “bad”. So the one they sold me was indeed no good. (Why they didn’t test it before they sold it to me is another question.)
But here’s the mystery: If the rebuilt starter motor tested “bad”, and it indeed was “bad”, how could it have cranked the engine with the experimental heavy guage wiring ? Any explantion for how a “bad” starter motor can crank the engine, but use way too many amps in the selenoid circuit?