[Badcatt]

I have a 1991 Ford F250 Extended cab 4X4 with a 7.3 diesel every morning when I go to start it the batteries are dead I jump it and it starts. The gauge shows that it is charging and I can start it the rest of the day unless I let it sit for too long then the batteries are dead again. I have brand new batteries in it and they are good. Nothing electrical is left on so I don't under stand what's draining the batteries.It has a external voltage regulator and I am thinking that is what it is. Wanting some input from you guys. THANKS

[TxGreaseMonkey]

Many auto part stores will test alternators and batteries for free. Remember, the voltage regulator is directed by the PCM when to increase voltage, depending upon a host of sensor inputs. It's possible to have problems with the PCM, but, like you, I suspect the voltage regulator. Should be a relatively easy problem to fix. Make sure all battery terminals and cable connections are clean. If they are severely corroded, no voltage regulator and alternator will be able to properly charge the battery.

[Stratmando]

DC Amp Probes are nice. Shows charge +, or discharge-, and amount of amps. Don't have to disconnect any wires and can clamp around wire, Like AC.
If you don't have one, or a meter:
Disconnect -battery cable, and hook up bulb between cable and post.(with bulb socket or test light)
It will probably light. Remove all fuses, Disconnect Alternator, Regulator, Anything, until bulb
goes out. Clock circuits.
Maybe I watch too many movies, Maybe someone put tracking device, and not going into sleep mode when vehicle stops, continues to draw power. Not Likely?
Be sure to plug in all connectors and fuses in Same place, same value.