Mystery cadillac illness

My 1994 Cadillac Sedan Deville has a recurring problem that we have thus far been unable to fully fix. Various lights will first come up (ie: airbag, antilock, etc). Next the display will read High Volts. This is followed by the car running poorly, resisting and acting as if it will cut out. We have taken it into the shop three times and the mechanics have exhausted themselves running diagnostics. They have done the obvious things (new battery and alternator) as well as checking the grounds, tightening any lose bolts or wires, and checking the computer. Any thoughts?

I would check the sense wire tieing between the battery the alternator for a bad connection. There is also a fusible link in the circuit. If the alternator sees a low voltage on that wire it will increase the output voltage to the battery.

Another drawing shows the powertrain control module with a feedback circuit in the alternator’s field circuit. Not sure if you model has that or not but it may be the problem if it does.