Puzzling Problem

[wj_xavier8]

Hello everyone!
Got a few questions in regard to my 72 f350 with a 360 FE. I guess the best way to describe what's happening is from the beginning.
I bought the truck a month ago. Asked the previous owner if the alternator gauge worked or not and he said no. Well everything was fine. Was working fine for a while. Well, I replaced the battery tray and upon reinstalling the battery, accidently put the leads on opposite terminals and blew the fusible link. I figured, no big deal, I've replaced links before. So that's what I did. Well....I was wrong.
After replacing the link...the alternator gauge started jumping back and forth at heavy throttle. Wouldn't do it just idling, but revving the engine, the needle jumps from center of gauge, to the "C" and back again. Over and over as long as I have heavy throttle. BUT as soon as it goes idle, it goes back to "c" and stays there. Well...the gauge jumping around didn't really bother me until the other night when I tried to drive and realised that when the gauge jumps around, so do ALL my lights. They pulse in correlation with the gauge jumping back and forth.

I figured, ok, maybe a diode in the alternator fried. Bought a new one. Installed it, put a ground wire straight from alternator to the negative battery terminal like the directions said. Cranked it up. Started fine. Went to Rev the engine, and it blows the fuseable link again. The same one that blew when I had switched battery terminals..after it blew that fuse, the gauge started moving to center the more throttle I gave it. At this point I'm really scratching my head.
I say screw it and go buy another fuse, AND a new regulator. Install both, check voltages. Battery is charging fine. BUT, now I'm right back to square one with the pulsing gauge and lights at heavy throttle.
Sooooooo basically spent $100 for shits and giggles.

PLEASE, for the love of all that is holy, someone help me so I don't turn this thing into swiss cheese in the back yard.

[cep62]

I may not answer all your questions , but back in the day the alternator didn't produce much at idle.
when you pick up rpm the lights get brighter and your gauge would show charge.

I suggest getting a volt meter to see what it's really doing.
it should put out around 14 volts at a fast idle , with the lights and heater blower on.

Too much isn't good , and of coarse too little isn't good either.

P.S
Welcome to the site.

[wj_xavier8]

Thanks for the welcome!
The alternator does pick up as throttle goes up. Checked voltage when in high throttle and it jumps. In correlation with the gauge and the pulsing lights. 14, 15, 17, sometimes 18, then back down to 14. All within a matter a second. I dont mind the dim lights at idle, but the pulsing lights is my issue. I go to drive at night and its almost like im flashing everyone I pass. Again, new alternator AND voltage regulator. So, unless one of those is bad out of the box, I'm at a loss. Lol

[DuckRyder]

My first inclination is that new regulator is bad. No way it should charge 18V. Is it a reputable brand?

After that - you’re down to tracing wiring.

[wj_xavier8]

Ac Delco brand I believe. I'll test the regulator this evening. I believe the testing procedure for it is to jump the connector so it goes full field. If it goes full field and doesn't waver, I'd suspect the regulator as well.

[wj_xavier8]

Well, went and got a replacement regulator. Installed it. Forgot to plug it in. Started the truck and the ammeter was working. Realised I didn't plug it in, plugged it in, and it's now doing the exact same thing. Makes no sense to me. Also, voltage at the battery at idle is 17v. My meter is a cheap.ass meter, I should get a new one, but it's still pulsing like before and the ammeter is still bouncing back and forth in correlation to the pulsing lights at heavy throttle.

[sargentrs]

Sounds like wiring harness?

[MadMike]

Check the terminals at the V.R. plug. Use a pick to slide each terminal out and verify they are not corroded or barely holding onto the wire with a single strand. From the outside my neighbors '70 F250 the harness looked OK, but once I removed the terminals two were toasted, one was a bad splice.
Verify the V.R. is bolted tight to the inner fender. I ended up replacing the craptacular selftapping screws with a pair of 1/4-28 bolts + nuts. I also went a little ham on putting 'ox-guard' on all electrical connections to prevent any future corrosion after cleaning mating surfaces to ensure a clean/tight connection.

Beg/borrow/steal a proper Digital Volt Meter and recheck all connections.