batteries draining while starting

[Blood_of_Tyrants]

BTW, a fully charged battery should read about 13.5 volts dc.

 

[Warthog]

yes with the key off, i got no volts on the black exciter wire. I got 12 volts on the red wire. both of these were with the key off and i checked them at the connector to the alternator.
with the key on both were getting 12v.
the link that you sent me didn't work but I have the TM that goes over that and the civilian haynes manual. so i should be good right? what kind of parts house can test it? i took the truck to advanced auto and they no longer use a load testing unit. they brought out some little box that is obviously a dummy version of a multimeter. you think napa would have it?

With the test you did with the key on and off, the wiring is okay. The alternator is bad. You can verify it by removing it and carrying it into Autozone, Oreilly's, probably NAPA. Just call and see if they test alternators. Those handheld don't really tell you much. When they are testing it tell them a 1984 Cadillac DeVille so they can plug it into the computer.

The link from DelcoRemy no longer works but the manual is attached in PDF format in the thread I posted. Here it is again.

 

[Barrman]

A fully charged battery cell should have 2.1 volts. 6 cells in a battery makes 12.6 volts in a fully charged battery. Most alternators have internal regulators in them that limit charging to 14.4-14.6 volts maximum. Anything below 14.4 with the engine running and no load put on the system means something is wrong.