Cant keep a charge

Have a 91 chevy pickup. Replaced the alternator and battery. Now the alternator and battery have tested good, but the battery only reads that it is getting 7.5 v while running from the alternator. I get the battery recharged and then it continually runs down. What could this be? Bad wiring or short somewhere? and if so, how do I track it down?

Get someone else to check that alternator.

Sounds like alternator. AutoZone or Advanced will test it for free. Could be bad connection. Check and clean grounds to block and chasis. Is there corrosion on battery cables. I would clean battery connections. Check power connection at starter.

Its impossible for an alternator that is only putting out 7.5V to test out ok. It should be somewhere in the range of 13.5V minimum up to about 15V. So was it tested out of the vehicle or while installed?

Did this truck still have a separate voltage regulator? Or is it integrated into the alternator?

If the main output lead of the alternator is putting out the proper voltage then there is a problem in the connection between the alternator lead and the positive battery connection. The fusible link may be bad possibly. If the alternator isn’t working in the vehicle then check the battery warning light and make sure it turns on when you turn on the ignition without starting the engine. If that light doesn’t work then the exciter for the alternator won’t work and there will be no field current built up inside the alternator. Power from the ignition switch ties to the light and the other side of it ties to the alternator ‘L’ lead for the ground. The connection fault will need to be found if that is the trouble.