After searching the forums I'm still missing something and can't quite get this figured out. The problem is the alternator doesn't seem to be charging the battery. I've replaced the alternator and the voltage regulator but no change to the situation. I'm thinking it's perhaps incorrect wiring at this point but also really don't know. I would really appreciate any insight and hope it's just something bonehead.

When the truck is off, I get 12.74 volts across the two battery terminals. This means it's a fully charged battery from what I've read. I start the truck, and instead of reading 13.5-14.2 volts give or take, I'm reading 12.50 volts. I turn on the lights to the truck and let it run for 10 minutes, now the reading on across the battery is 12.24 volts. So that battery is discharging and not getting any help from the alternator I'm reasoning. I've tried reving the engine as it sits idling up to 2,500 rpm to see if perhaps the alternator just isn't turning fast enough because I had read that can happen with older vehicles, but as I rev the engine and hold it the volts drop to 12.22 volts. If I turn the lights off the voltage jumped to 12.47 volts. After I turned the truck off after 15 minutes of idling I waited maybe 20 minutes and checked the battery and the voltage across the battery was back up to 12.70. I thought perhaps the connections were corroded so I just cut the old connections on the three wires going to the A, S, and F terminals on the voltage regulator and put new ones on the wires. No change, same situation. When I test the voltage from the negative on the battery to the BATT on the back of the alternator I get the identical reading as across the two battery posts. Same goes if I touch the A wire as well at the voltage regulator. The two belts on the pulleys are brand new and nice and tight, so not slipping.

I'm wondering where to head next. Here's some more info that hopefully helps. The BATT terminal on the back of the alternator goes to the A on the voltage regulator and the battery side of the starter solenoid. The FLD terminal goes to the F on the voltage regulator. That's it though. The STA was initially setup open so I left it that way. On the voltage regulator there is a green/red wire that goes from the S through the firewall into the cab and under the dash. At this point I'm wondering if that has anything to do with my situation? The I terminal isn't connected to anything. Now, the dash ALT gauge was already disconnected by the previous owner so I'm wondering where that green/red wire goes and if it needs to be connected to get things working.

Thanks a bunch for the help, this is hopefully simple and I'm just missing something and didn't need to even buy the new alternator and voltage regulator, but with both of those being new hopefully that helps rule things out.

 

If the alternator isn't putting out, the diodes are probably bad.

This would be a good time to pitch the old 1G alternator and the external voltage regulator and install a Ford 3G, internally regulated, alternator. I have a 130A 3G alternator on the 240 in my '69 F100.

130A 3G will have (2) holes inside each of the 3 pairs of ribs. The 95A 3G will have (4) holes in between the pairs of ribs.

 

Here's the wiring diagram, good luck and skill. http://www.fordification.com/tech/wi...rWiring_01.jpg

 

We'll I figured it out thanks to something Franklin2 posted. Turns out I was giving the previous owner too much respect for having things in working order. Here was the problem: there was a plastic wire holder that made plugging in the three wires into the voltage regulator quick and foolproof. Instead of having to trace each wire to its origin and then make the determination of whether to hook it to the I A S F connection you just plug it in similar to when you plug in trailer lighting. I assumed since all the connections looked equally old that this setup had been working for years and years right? Wrong. Apparently he switched from a three prong A S F to a four prong I A S F. In doing so the S now went to the ignition which was fine with the three prong. With the four prong however the green/red wire going to the ignition now needed to be switched to the I post. As soon as I did that and ran a new wire from the S to the STA on the back of the alternator I had 14.23 volts across the battery with the engine running. When I bought the truck I needed to replace the battery and now I know why.

 

Glad you found out the problem and fixed it.

One thing to note for others with a similar no charge issue; always check the health of the battery to Alternator, Batt to Ground, and ground strap cables, and that the enda or each are properly secured. This doesn't apply to this scenario, of course, but thought I'd offer the advice.