more starting problems

I have recently purchased a 1986 Supra which has a starting problem no one can fix. If the car sits for an hour or more it starts fine and runs great. If the car has warmed up and run for twenty minutes or so and I turn off the ignition, it won't start for at least twn minutes or so. The starter doesn't seem to be getting any power form the battery as it doesn't even try to turn over. I have had the battery checked and it's good; I have replaced both the starter & alternator; the garage has checked the relays and rewired from the battery to the starter; I have even had the ignition module replaced and still the problem persists. Any suggestions or feedback would be apprciated. Thanks.

Make an enlarged copy of the wiring diagram and highlight the starting circuit. Check the engine ground strap to make sure it is properly secured with clean contacts. Disconnect the coil wire and use a meter to check the wiring for voltage when the starter is not turning over the motor.