While on a trip, I noticed the voltmeter in the dash drop to around 12 or so volts from the usual 14ish. A week later the battery was dead, it was 6 yrs. old so I bought a new one. Of course the next morning the truck wouldn't start, dead battery. I then charged the battery up over night. The next morning I started the truck, with the motor running, I have 12.8 volts across the battery posts. Measuring from the positive termanal to a ground on the motor or frame, I get the same voltage. With the motor off I have about 12.5 volts. I have 2 plugs on the alternator, I've removed them, blew them out with air and applied dia-electric paste. No change. It's only been less than 1 day since the over- night charge, but I'm sure the low voltage is a problem. Thanks in advance.

 

If you have the 2G alternator one of the plugs on the back may have shorted internally draining the battery overnight.
At least it has happened to me.

They make an aftermarket replacement alternator pigtail that any well stocked auto parts store should have. You cut the old one off and attach the new plug.

I finally got sick of trying to burn down my truck and swapped to a later 3G alternator using one of Ryan's harnesses from fordfuelinjection.com

 

which plug was it? I guess you mean that the plastic between the individual leads has melted creating a short between contacts. I'll go check this.
thanks

 

That is, if it discharges w/ the alternator unplugged.

Otherwise it could be the alternator, but the simple check is to unplug the alternator and see if there's measurable voltage drop overnight.

See this thread: https://www.ford-trucks.com/forums/3...st-burned.html

 

I really need to fix this thing today. another thing we noticed is that there is about .5 amp drain on the battery and pulling each fuse individually didn't stop the current flow.

 

Do as I said and unplug the alternator.
If it stops it's the alternator, if not, the pigtail is only about $10

 

I'll unplug and wait overnight, but in the meantime......
should unplugging it stop the current drain?

 

Well, there shouldn't be any drain....

But if the alternator is shorted internally, Yes.
If the plug is bad there will be no affect.

I did not know from your first post that you had a way to measure.
There is always some tiny draw for things like radio memory.

 

If you have 12.8 volts with the alternator running, either you have a bad connection to the alternator, or it is broken. Running voltage should be close to 14.
Check the green with red stripe wire coming to the alternator. With the ignition on, it should supply 12 volts. This turns the alternator on. Check both ends of all the connections, including the plugs. Look for corrosion, or melted plug. The next step is pull it for a bench test at about any parts place. Since the battery discharged overnight, I would suspect a bad diode inside the alternator, but usually a bad diode will still let it have the correct output.
If the alternator is bad, you can replace it and splice in a new plug, or upgrade to a 3G. The 3G doesn't use a plastic plug, and can produce a lot more amps than the 2G. Nearly everything you need is available in a upull junkyard for a few dollars.
Read some of the old threads about this upgrade, and be sure and use a fuse. Big potential for a fire with the old stock 2G or an improperly wired 3G that doesn't include a fuse. Couple of years ago a local lady burned down her house when her 2G alternator set the truck on fire in the attached garage.
Good luck Frank

 

I'll check the green wire now, should it be disconnected to check?

 

No need to disconnect it. Should read 0 until ignition is turned to run, then it should be hot. This is just the on and off power to the alternator.
Frank

 

First off, the battery is down to 7.6 volts, this is a new battery and was at 12 last evening. I don't have a green w/red wire, it this the heavy gauge wire or the smaller size? checking both plugs off the alternator with the switch on, several wires have the 7.6 volts.

 

the small gauge green wire reads the small as battery voltage when switched on. the voltage is actually 11.5. I can't explain that, except that meter may be crap, it's a new digital one though. the larger plug does show signs of melting. I'll go replace that now if I can find one, I"ll check autozone and the junkyard. It's not clear if a auto parts alternator check will answer all the questions. I'll try to find a $15 pick and pull ford alternator and try that. I don't trust the $100 auto parts store alternators..........
thanks for all the help so far.

 

I would get the battery unhooked and get it on a charger. You are going to kill the battery or at least shorten it's life a lot. The alternator is not designed to charge up a dead battery. You could kill the new alternator when or if you replace it.
Good luck Frank

 

Just picked up a new plug from autozone and a alternator from pick and pull. the alternator was from a 1990 6 cylinder for $20, my truck is a 1989 F-150, 302FI. I'll post the results soon