Cadillac Repair: Cant start have 2 caddys electrial prob /w dash, electrical schematics, cadillac dealer


Question
Hello I have 2 91 Caddillac Eldorado's and Im usiing one for parts for now to get the other one running
One ran fine even had it diagnosed by Cadillac dealer. They said the car was fine.
Now the other week It started running rough like there was some bad gas so tapped the pedal and it ran fine until the next day I went to go somewhere, warm the engine up it started the same thing running rough then just died, but along with that the whole dash display and information console just blacked out.
Now if I give it time every once and a while the display's will come back up but once I try to start the car you hear some relays click then blamo no more display. I put in a new starter also  double checked if any wires were shorting or melting but no problems I can find even after the dash turns off you can still hear the relay near the passkey still triin to start the engine but seems like somthings shorting out but what? You can hear the fuel pump running also when theres no dash.
I also changed out the ECM (switched and kept the same EPROMS with same cars) And put in a new BCM. Wonderiing if it could be the PCM.
I also took off the battery terminal and touched both terminals to reset the computers.
I try to run the diagnostic but the dash will only show for 3 or 4 seconds until it shuts back off.
Im open to any sugestions? THanks Also Is there any alterniative in making theese cars run with a better easier computer system more basic. I appreciate your time. Sincerely, Justin
PS: Great cars love 'em bad computer setups.

Answer
Never ever do this :

I also took off the battery terminal and touched both terminals to reset the computers.

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