98 S-10 blazer starter problem

I am totally stumped and so are the dealers.
My wife was driving to work one day last month and lost all her lights, then the car just stopped. I had i towed home and thought perhaps a
new battery would fix it. My son in law discovered the starter was gone so I picked up a re-man and he installed it--voila! It seemed to fix it...but after it had run for 15 -20 minutes a loud screeching sound began which he eventually traced to the starter. It seems that all by itself the starter would re-engage (or perhaps not disengage) and it pretty well cooked it. We took it back and exchanged it for a new one and thought we had solved the problem but after 20 min or so it began to do it again.
Next we replaced the ignition switch as suggested but that didn't solve it either. We tried an new switch but that didn't change anything either. We have also checked and changed the relay.
We have searched to see if someone had installed a remote starter but there is none. His code reader doesn't show
The GM folks have no idea what the problem is and say they've never heard of such a thing.
Meanwhile the car sits in the driveway... The only other source of power to the starter is the the instrument cluster per the schematic. CAN ANYONE HELP PLEASE!
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Dave wrote:

Do u have The KEYLESS REMOTE STARTER ? If So is it Malfunctioning. 20 minutes is about the time they are set to turn OFF the engine, Cud it possibly Trying to RESTART the vehicle after 20 minutes ?

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Proof read !

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Do you have ON-Star?

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lights,
it
solve
Which engine and trans? Trim level? Any non stock options?
Try this test. Turn the key on but don't start the engine then disconnect the small trigger wire that goes to the starter solenoid. Connect a volt meter (or test light) between that connector and ground. If voltage shows up after the 20 minutes then there is something on the start circuit backfeeding that line. It should be dead unless you are turning the key to start the engine. If it doesn't show voltage on the wire hook it back up and then try starting it and test it the same way again.
The problem is I don't see much that feeds off that line in start position that has any type of timer circuit on it. Leads me to think that there is a thermal problem in one of the modules or relays. It takes about 20 minutes for it to heat up and trip on. Since you have the schematic look for the Hot in Start and Run items. Look for a common power connection point.
As a temporary work around you could connect a switch in that wire to the started solenoid and just shut it off once the engine starts. At least that would allow you to drive the vehicle until you have some spare time to play with it.
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Dave wrote:

Has anyone checked to see if the wires that run off the starter (Fused links included) up through the tube have not melted together? I had a similar problem with a 88 2.8 S10 I still have where the S-terminal wire was slightly melted into the fused link.
Next question. How does the ring gear look after all this?
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