I have a 76 F150 4WD manual with a 360 that won't hold a charge when driven 10+ miles.
Back story on the truck: it was my Grandpa's farm truck and saw A LOT of hard times and suffered even more abuse before being put to pasture in '02 (parked in a field and abandoned). I pulled it out of the field and at this point have it running and have driven it short distances to tweak issues and see what else needs attention. I finally got it where I trusted it enough to drive it to the gas station about 10 miles away. Up to this point I had driven it shorter distances and it would start right up after being shut down. I stopped at my parents house near the gas station on the way and when I went to start it back up the battery was dead. A couple of minutes on a charger and she started right up. I've done some tests and anytime I get over 10 miles on the odometer and then shut the engine down the battery is dead but restarts after a very short charge on the tender.
It has a complete new ignition system including replacement of worn or exposed wires in the harness. I have also fixed wires throughout that were in need of attention. It has a new distributor, alternator, voltage regulator among other parts. I'm at a loss on what the issue is here. Grounds have all been checked and a couple have been added. The new alternator was removed and tested (Putting out 13.8- 14.2). Lights all work. I don't think the stock voltage gauge is working. It does not move and stays right in the middle of the gauge.
Any ideas or input would be appreciated. I have noted that on the voltage regulator the field and battery studs are hooked up per the wiring diagram in the Haynes book but the wire running off of the Stator stud goes back towards the firewall unstead of straight to the VR. The "I" spade on the VR is empty.

 

Well it's not charging if the battery is dead (obviously). Be sure to charge the battery thoroughly back up overnight to keep it from being damaged.

Modern maintenance free batteries, and AGM/VRLA batteries, due to the construction of the plates have a resting voltage of 12.8 volts at 80F, the 12.6 voltage figure is correct for older type conventional batteries with fill caps for the addition of distilled water. 0.2 tenths of a volt doesn't sound like much but would represent a battery that is only 75% charged. It is important to keep batteries fully charged whenever possible.

http://jgdarden.com/batteryfaq/carfaq4.htm

It is possible the battery is bad, how old is it? Best to have it tested. If the battery is known to be good turn all the lights and accessories on and heater blower to load alternator up, and run the RPM up to around 2000 or so and measure the voltage at the battery terminals. Should be somewhere between 13.8 to 14.2

These are available online for about 10 bucks from that auction site they work great for keeping an eye on voltage from idle to cruise. Plugs into cigar lighter receptacle.

 

You'll have to check the voltage when it's idling.

Lead-acid better, fully charged with it's "surface charge" removed by turning the lights on for a few seconds and then back off is 12.6 volts or slightly above.

"Abosorbed mat" sealed batteries are around 12.8.

When running, you should see anything from 13.0 and up, as the stock alternators on these engines weren't exactly high-amperage.

I don't have my Motor's manual around, so I can't check the alternator wiring, I'll try to remember when I get home.

 

X2 on the bad battery. I have seen bad batteries do all kind of strange things. Assuming that everything is connected correctly, it sounds as though there is a parasitic battery drain. Disconnect the ground cable at the battery and connect a multimeter, set on amps, between the cable and the battery. If there is a draw on the battery, you can disconnect components or fuses one at time to locate the bad circuit. New parts can also be malfunctioning. Good luck.

 

I'm at the firehouse today but I pulled the battery last night and will get it tested tomorrow. Before I pulled it I started the truck and with it running I pulled the negative clamp which killed it. That's a sign of the alternator not working if I remember correctly. I had the alternator off and tested and it tested good. Thinking maybe the wiring is messed up somewhere?

 

if I recall correctly, disconnecting the battery while it's running is also a sure-fire way to blow the regulator, especially the thin electronic ones (the older thick ones were actually mechanical).

Old-style big one:



newer electronic version:

 

[QUOTE=Krewat;16548369]if I recall correctly, disconnecting the battery while it's running is also a sure-fire way to blow the regulator, especially the thin electronic ones (the older thick ones were actually mechanical).

That'd be my luck!!

 

Had the battery checked and it tested good. Took the electronic voltage regulator off and replaced it with the old mechanical one. Started it up and drove it for about 20 miles. Shut it down and it started right back up; before it would have been dead. Voltage tester on the battery while running shows 13.9 or so.
Thanks for the input and suggestions. On to the next undertaking.

 

Excellent! Thanks for the update

 

Now, put the electronic one back in and make sure it's really bad

 

Some years ago I built a 68 Mustang, 289 tri par, 4 spd to make a nice street cruiser, after getting it running and tuned volt meter showed 14.1 so charging system was working. Drove it 20 miles to a buddy's house and the battery was down, test showed it wasn't charging and the new electronic regulator was bad, took it back to the parts store and they said no warranty on electronics so bought another one. After installing it showed 13.9 so we're good to go, drove it 20 miles back home just to have another low battery, that regulator had gone bad, again no warranty on electronics. When to a different parts store and all they had was the new electronic regulators so I got one from them and installed it with voltage showing 14.2, drove it 8 miles to get fuel and it nearly didn't start, another regulator gone bad with not warranty. Went to my buddy's and got a old point type regulator, cleaned it up and installed it, 14.1 volts and was still working when I sold the car a couple years later.
Don't know why the electronic regulators wouldn't hold up but I've never liked them since then.

 

It's really bad. 8 miles, no start.