Hey all, new poster to the forums, but long time lurker.
My 66 F-100 isn’t charging. I have read through every post I could find. A breakdown of what’s going on and what I’ve done:

• I’m getting 12.4 amps at the battery, 11.5 amps with the headlights on.
• I’m getting 12.1 amps at the A terminal on the Voltage Regulator as well.
• I have replaced the alternator with a 70a Tuff Stuff alternator, and Voltage Regulator from summit racing
• I have replaced the Voltage Regulator wiring harness with one from Dennis Carpenter.

At this point the only think that I can think of is that I have a draw somewhere? The battery will hold a charge even sitting for a few months, so it’s not drawing when it’s parked. Any ideas on how to get me up and running would be great!
Thanks!

 

I think you mean 12.4 volts at the battery. What is the voltage output at the alternator when you get that reading?

 

Alternator voltage output should be measured directly at battery posts with all headlights and accessories, heater fan etc on, and engine @ 2400 RPM

 

Check wiring to make sure when you replaced it all that everything is correct.

 

I would also check the wiring harness with a multi-meter for continuity on each circuit. I bought a new alternator harness a few years ago for my '69 mach 1 that was made wrong and wouldn't trigger the alternator to charge. Is the ALT light on in the dash? It is a balanced circuit with the battery on one side and the alternator on the other. When it's on that means the battery is powering the light and the alternator is not putting out voltage, which is what it sounds like as you should be getting approx. 14.2 to 14.5 volts at the battery when the engine is running above an idle.

 

I thought I had a problem with my battery and alternator, but turned out I needed a new ignition switch.

 

Thanks for the replies everybody. I have checked my wiring on the alternator harness, and it's all correct. I am getting 12v at the alternator. I will check continuity throughout the harness and start hunting elsewhere. Someone else has suggested the ignition switch, and possibly the fusable link coming from the alternator. I will get back to you all with an update!

 

How old is your battery? Just for kicks, run by a parts store and have them test it. Could have a bad cell

 

I second this. I replaced the alternator, regulator, and harness all at once on my '66 after 20 years of sitting. After getting it started, the ALT light stayed on and it wasn't charging. I checked all the connections to make sure everything was correct and tight. After that, I used a multimeter and checked each wire run on the new harness against each wire run on the old harness for continuity. I found that there was some kind of defect in the plug for the voltage regulator on the new harness. The vendor made good on it and replaced the harness. The second new harness worked perfectly and the alternator was charging. The problem could be cause by a few things, but I wouldn't rule out the harness just because its new...