I'm working on a '72 D-100 with a charging problem.

The thick black wire from the alternator was grounding out against the valve cover, so I patched in a new wire and installed a new voltage regulator.

All connections on the bulk-head connector look good.

Even though the alternator tested good, the gauge does not work and the battery still does not charge.

What else should I check? Can a bad gauge cause a charging problem?

A couple of things.

Does that have an electronic regulator and 2 field wire alternator?

The reason I ask is my Dad had a 75 Gran Fury that refused to charge after changing everything out. He converted it back to a mechanical reg and single field connection alternator and it was fine. (those new fangled electronic regulators are junk with assorted profanities throughout )

A few years later he had the dash apart because the ammeter never really worked that well on it and he decided it was time to find out why. It turns out the connections were all green on it. He cleaned them up and low and behold the ammeter actually showed charge.

That got him thinking about the electronic regulator so he hooked that stuff back up and it worked fine.

He has a background in electronics and figured that the regulator sees a fully charged battery as resistance and shuts down the alternator. The problem is it saw the resistance from the bad ammeter connection and did the same thing.

Sorry for the rambling.

The other thing is if it has the older style ammeter and it goes open, it won't charge. On those all voltage from the alternator goes thru the bulkhead, thru the ammeter and then back thru the bulkhead to the battery. I forget what year they went to a shunt but I don't think they can cause the same problem except for what I described above unless it completely melts down and that usually results in a dash fire. Might be worth checking tho as you did short out the main alternator wire.

Make sure the regulator if it is electronic with a 2 field wire alternator, is well grounded as that is how it controls the field voltage (varies the ground). No ground, no charge.

Kevin

Truck should have dual field alternator and electronic regulator. I am not positive on a 72 but as said if the gauge on the early ones go you can get a no charge situation. Pull the cluster back or poke your head under there and take a look at the gauge. Confirm power to all connections with meter and look for any melted wires in case something was not noticed on initial inspection of system. If you have another regulator laying around give it a whirl.

a bad amp meter will stop charging. seen it before and it makes sense since all the amps flow through there.

you can verify this by testing the back of the alt, output for voltage, and I bet you see 14 volts for charging. it just isn't making it anywhere.

as said above, if you want to, get behind the dash and check you probably have 14 volts on one side of the amp gauge and nothing on the other.

you can of course bypass it, or run a wire from the back of the alt directly to the battery to get it charging for now.

Some simple things to check:
Make sure you have 12v at the alt. stud and not just 12v potential. I have used a meter and saw 12v at the alt but soon as it loaded or the Alt tried to produce 12v , it would go open . I discovered just one strand of copper was connected in a maze of green corrosion.
So use something that draws 12v , ground it on the alt and see if there is actually 12v there . I use an old heater motor .
Another thing to try is: with motor running , lay a screw driver to the back bearing of the alt and see if there is a strong magnetic draw. if not , alt is not charging. you can by pass the regulator for a sec by what is know as flashing the alt . place a screw driver from the hot 12v wire to the teenie weenie stud that sticks out the back . Its like a # 6 screw or something . just touch across and if that's the problem you will hear the alt cut in .
Most likely you have trouble somewhere back the line . maybe under the dash at the amp gauge . also try another voltage reg . new ones have been know to be bad too .

Is there a way to check the voltage regulator?

Should there be continuity between the 2 pins?