Good morning all
I have a 1994, F150 Ex-cab, 4.9, M50D, and a couple of weeks ago my truck developed a short that would drain a fully charged battery overnight. This is a truck that is driven at best on weekends and will sometimes go two weeks without being driven and has never missed a beat, always fired right up without any problems.
First thing I did was change out the battery come to find out my load tester wasn’t working so now I have a new battery in my truck and a perfectly good one sitting in my shop.
So then I started unhooking the aftermarket stuff CB wire, outside temp. thermometer, still no change. So using the negative cable and a Multi-Meter and with everything unhooked I measured a 3.5A draw, started pulling the under hood fuses first nothing there. Before I crawled into the cab and started pulling fuses I was just checking a few things under the hood unhooked the Alternator and the draw dropped to zero. Plugged it back in and the draw came back, unplugged it again this time I waited for a couple of minutes plugged it back in nothing the draw stayed at zero. Hooked everything back up started the truck let it run for a few did the check again the 3.5A draw was back went thought the same process as before and got the same results.
Question is, is my Alternator the draw? Or did it go to zero because by unplugging the Alternator I interrupted the current flow? By leaving it unplugged did I allow something else to reset if so what could that be?
Thanks
Tim C

 

I would look at your frame ground...disconnect clean and re-connect all the grounds

 

Your alternator diode bridge is shorted, so current is flowing back into the alternator and killing your battery.

Time for an alternator rebuild or hit the junkyard. I don't recommend buying a "reman" alt from a parts store.

 

Thanks looks like its time to change out the alternator.
Tim C

 

Having it rebuilt is usually the best way to go. And normally, at least in my area, it runs between 40 and 60.