Cadillac Repair: 1991 Caddy Seville Starting Problem, starter solinoid, minuits

Question
Dear Bill,
I have an old 91 Seville.  It generaly runs well.  However, when it has been running for more than half an hour (i.e under the hood is hot) if I stop and try to re-start the car, the horn sounds when I turn the key and the engine will not turn over (feels like the anit-theft is engaged).  I get no error messages on the computer display.  If I pop the hood and wait for 10 minutes the car will start as normal. I have recently installed a new battery and cleaned the earth wires but this made no difference.
Hope you can help, as this minor flaw makes the car tricky to use for short trips!
Kindest regards
Alan

Answer
Hi Alan, There are many times that an aftermarket alarm will cause an engine not to turn over or start. The fact that you wait for something to cool down would suggest a module or solinoid is going bad. When the engine won't start you will need to test the circuits with a test light or voltmeter and see where the problem lies. Start by checking for power at the starter solinoid with the key in start position. It could be a bad starter solinoid or starter if there is voltage. Continue tracing the circuit back until you locate the problem. The fact that the monitor doesn't display wait 4 minuits indicates that the ignition key and cylinder are probably good. Cleaning the grounds/earth wires and replaceing the battery was a good place to start. Now you need a wiring diagram to continue the diagnosis process. Bill