Auto Parts: 79 f150 battery drain

Question
I have a 79 f150 the battery is brand new the alt. has been checked and checked good. Everything works and runs great for about 3 to 5 days then the battery will be totally dead if charge it up everything fine for 3 to 5 days then dead again.Any ideas on what could be wrong?

Answer
    There could be a bad voltage regulator, which is mounted near the battery.  Or there could be a bad diode in the alternator.  It would still put out when it was running, but it would drain the battery when sitting still.  These old Ford alternators are pretty simple, though, and not prone to this sort of failure.  If you could get another alternator to try, I would.  Lastly, there could be a short somewhere in the wiring.  I would get a milliammeter, pull one of the battery terminals off, and then connect across the gap with the meter.  Make sure first that EVERYTHING in the truck is off, even the overhead light (close the door).  Have the key in the off position and, if it has an underhood light, take the bulb out.  If you show more than a few milliamps draw across that gap with everything off, then there is a short in something.  Then you'll have to go around the truck looking for it.  The horn switch and relay, the cigarette lighter, and the stoplight switch are all good places to look since they are not turned off by the ignition switch.