1983 Toyota Supra Neither window motor operates

MARY R

MEMBER
1983 TOYOTA SUPRA
300,000 MILES

I have 12V to window motor but motor wont operate. When I jump to battery the motor works every time. Shouldn't I be able to rule out the switch, the relay and the circuit breaker since I do get 12V at the motor connector? Resistance and continuity to ground at the switch checked out OK. I have duplicate parts of every component and swapped them out with no difference. The strange thing is when I operate the switch and measure across the motor the 12V is reduced. It's too unsteady to get the exact reading. Is this normal? Thank you.

2 Replies

CARADIODOC

MECHANIC
33,916 POSTS

Try using a test light instead of a voltmeter. It sounds like there is a high resistance break or bad connection. All you need is a little carbon track to let enough current through for the meter to pick up, but enough current to run a motor won't get through. The test light needs much more current to work so it will give more accurate readings. The clue is that 12 volts is going lower when you try to run the motor. Some voltage is being dropped across the bad connection leaving less than full battery voltage for the motor. Broken or frayed wires between the door hinges would be a good suspect.