Voltage regulator or alternator??

Hey guys. Working on the yellow Mach 1. Found brand new alternator not charging. Returned it today got another one. Tested at store was good. Brought it home installed and it’s not charging. I unplugged voltage regulator and jumped it out and still only 12 volts at battery. Can a voltage regulator burn up an alternator instantly?? The regulator is brand new and the alternator is brand new.  But not charging.  I have never had a voltage regulator hurt an alternator. Always overcharged when they went bad. Anyway to test a voltage regulator with a meter?? All wiring is correct. Just wondering if I got 2 reman alternators that we’re junk??

Brand new regulators seem to have a high failure rate. A bad regulator will either make an alternator overcharge (when the contacts are stuck together in electro-mechanical regulators), or not charge at all when no voltage is applied to the field wire to the alternator.

Does your battery ground cable run from the battery to the lower screw on the regulator and then to the engine block? A good ground between the alternator and regulator is essential.

Are you sure the wiring is correct? There are two different wiring methods and schematics, one for cars with gauges and one for cars with idiot lights. When you turn the ignition key on check for battery voltage at the "I" terminal on the regulator if the car has idiot lights, and at the "S" terminal if the car has gauges.

If I can just chime in here, last summer on a hot day, I noticed my near new voltage regulator was showing 15V on the brand new set of aftermarket gauges. Without going back to check, someone far more knowledgeable than I suggest that the reg was fried. I have just purchased and installed a solid state one that is correctly painted and with the correct logo for the 71. The volt gauge now shows a solid 14V, so I would suspect that reg was fried. If I can find that link, I'll post it later. Oh! it was Virginia Classic Mustangs that sell them.

On the grounding issue, please make sure to scrape the paint off from under the tab connection at the reg. I found that out too.

Little things sure get frustrating!

Geoff.

Voltage regulator and alternator are both new. Wired up same way came off. Wires really can’t go any other way they don’t reach. Paint under regulator is scaped off. Brand new battery. New battery wires. All grounds are good. Gonna take regulator and alternator to autozone tomorrow see if they can test both.

Alternator and charging system is pretty simple. Alternator should not go bad that quick regardless. Even with not voltage regulator it should run for a bit at more than 12 volts. Just frustrated. Stupid stuff. No reason this shouldn’t be working correctly other than faulty parts.

Alternators are not self energized, like a generator is. An alternator needs voltage to energize the field windings before it starts to put voltage out.

Alternators are not self energized, like a generator is. An alternator needs voltage to energize the field windings before it starts to put voltage out.

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Hey don, do you know by chance which wire should be providing the 12 volts to the alternator??

There is a "STA" terminal with white/black wire going to it.

There is a "FLD" terminal with orange/blue wire going to it.

There is a "BAT" terminal with orange/black wire going to it.

The BAT terminal always has voltage to it, connected to battery.

This car does not have gauges, just idiot lights.



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Orange/Blue doesn't sound right to me.

Orange/Blue doesn't sound right to me.

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You can see the pic of new above. And old below. Its orange with something but its hard to see.  It has to be wired right. Just unbolted it and bolted new one on, same exact way.  It worked fine with the old one.  Orange wire going to FLD

They wont reach any other way.

Orange/light blue stripe to FLD, black/orange stripe to BAT, white/black stripe to STA.

Power to energize the alternator comes from the ignition switch on the light green/red stripe wire and connects to the "I" terminal on the voltage regulator (on cars with idiot lights). The regulator then connects the voltage from the ignition switch to the FLD wire and terminal.

Just got alternator checked again and its good. Reinstalled everything and checked voltage to green wire. It’s all good. Found an old regulator in the garage and threw it on. Everything worked! Battery charging at 13.6 volts at idle. So now to return the new regulator and try again!! These aftermarket parts are ridiculous!!! Bad alternator and voltage regulator brand new right out of the box!! Talk about a pain in the ass!!

Just got alternator checked again and its good. Reinstalled everything and checked voltage to green wire. It’s all good. Found an old regulator in the garage and threw it on. Everything worked! Battery charging at 13.6 volts at idle.  So now to return the new regulator and try again!! These aftermarket parts are ridiculous!!! Bad alternator and voltage regulator brand new right out of the box!! Talk about a pain in the ass!!

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At least the regulator didn't decide to full field the alternator and spike the entire car with 18V, taking out your brand new MSD 6AL box. Stupid $15 regulator cost me $75 in repairs from MSD. I now only use Motorcraft electronic units, mostly scavenged from junkyard crawls.