I have a 84 seville that wont stay running. The problem is it will run for about 15 to 20 minutes during a drive, and then begin to loose electrical power to the whole car. It acts as if it is the alternator going out but it isnt that or the battery. They both have been changed and tested. I checked the voltage while the car was in park and running. I got 12.04 volts, and the 20 minutes later I got 11.85. It is as if the alternator is not working, and yet it tests good. Is it a relay in the charging system or what?
Yeah it sounds like the alt isn't working, Like you said. Maybe the regulator is bad, or you have a bad connection to the rest of the charging system... I know that's not much help but no one else is saying anything.
I don't think your alternator is charging properly...your battery should be reading 14 to 14.5 volts. That's a proper charge to your battery. Maybe it's your voltage regulator?
With a low charge to your battery, the more power your car uses, the battery can't keep up with the demand on it with such a low charge. :drinker