Intermittent charging

[DustyDave]

1973 Cuda. When the car is running, the stock dash battery gauge always is just to left of center showing discharge. The dome light and radio brighten and dim alternately every few seconds. There is an aftermarket set of gauges with a volt meter which normally shows no charging, but occasionally jumps to show charging for a second or two….then back to nothing. The alternator looks new. I’ve only had the car about 2 years, but it’s always been this way. Dash lights don’t work. Dimmer switch doesn’t work. I tried a new voltage regulator, and no change. Has the stock orange box. Is it the alternator?

 

[Chryco Psycho]

More likely to be a bad regulator or the reg is not grounded properly

 

[Challenger RTA]

Start with the diagram below. Where the gauges are hooked up can make a difference on the reading.

Inspect bulkhead connector wire 16 and 18 for bad or burnt connection.

 

[Challenger RTA]

You have more than one problem. 1 check the foot dimmer switch plug. It is more than likely melted. There are replacements made for it. Time to put in a headlight relay circuit. It will remove a great deal of load from the bulkhead connectors.
There is a a Good Bad and Ugly to this.
The good: 1 You no longer have this load going through the bulkhead. 2 the load is not going through the foot dimmer switch. 3 Bright and reliable lights. 4 Minimizes chance of a fire hazard.
The Bad: 1 the Amp meter will no longer detect the load. Who cares? ( with alt by bass) 2 the load should be connected to the alternator load. Meaning an alternator bypass needs to be done. Because the alt is still feeding that load thought the bulkhead connector. The alt feed all loads through splice one that is under the dash. That is unless you feed it from the back of the alt instead of the starter relay as shown. ( I don't agree with the diagram). Or run a 6GA wire to the starer or stater relay. Here again using a fusible link or circuit braker protection on the back of the alt. In theory the the diode in the alt should blow
( as someone here has stated) in case if a short but why take a chance!
The Ugly 1 some don't like the idea. 2 If you don't conceal the 6GA wire it can be seen. That open an an other issue. Feeding the load from the alt or leaving the original wire in place. Moving it to the point where the alt is connected. Hear again fusible link it was never fuse before. Yes. Connect the the original link. Parallel or split? If you split your fuse box split.

 

[Challenger RTA]

2 Dimmer switch power and ground need checked.

Read this
:

Dash lights a Brighter possibility

Dash lights a Brighter possibility. Took gauge cluster out to clean all connections. Found some light sockets rusted. Cleaned all cluster and switch terminals and grease. Had the dimmer switch out and jumped with a wire while working on it. I think I still have a problem with the socket for the...

www.forebodiesonly.com

 

[Challenger RTA]

More likely to be a bad regulator or the reg is not grounded properly

And yes check the grounds on the motor, chassis by the battery, dash mounting bolts and the alternator mounting bolts. Be sure they are clean and tight. The battery cable can corrode an 1" inside the insulation and cause a problem. As far as the dash lights the ground passes through 3 ground points. 1 the dash mounting bolts. 2 the screws for the mounting light bar 3 the light socket.

 

[Bret Schneider]

Here's a pretty good write up I came across on how to check the charging system.
As others have suggested, the dash lights / dimmer issues are a separate problem.

Make sure the VR is grounded. Scrape the firewall around the bolts, the back of the regulator case, use star washers
Check the alternator and field wiring by "full fielding" the alternator
The way these work is, the ignition switch (ignition run) feeds power to one field terminal (does not matter which one, you can switch field wires)
So power goes to one field terminal, THROUGH the field magnet, and back out on the GREEN
The regulator controls it by controlling the "amount of ground" so to speak on the green wire.

1---At the regulator connector, ground the GREEN terminal. Run the engine while monitoring battery voltage, say, at the starter relay or other battery "hot" point. Bringing up RPM should cause battery voltage to rise. If it does not, clip your meter to the alternator stud and try again. If it goes way up there, but not at the battery, your charging line is not actually continuous to the battery. If voltage does not go up at the alternator, but you DO have battery voltage (12.6) there----------------------go to 2

If the battery voltage DID go up in this test, check to be sure that the regulator harness connector and the regulator terminals are clean, and DOUBLE check that the regulator is grounded. Hook everything back up "normal" and recheck. If it does not charge, replace the regulator.

2--Might be a field wiring problem. Engine off, switch in "run", pull the green field wire off at the alternator, and clip that alternator terminal to ground. You should get a small spark. Measure voltage at the opposite field terminal to make sure you have battery voltage "under load." If you do, start the engine, and again check if charging voltage comes up. If not, you have problems with the alternator.

If voltage DOES come up, and did not in test 1, you have a field wiring problem somewhere

Basic diagram:

All you have is, the regulator "I" terminal (middle one) goes to switched 12 volts, along with ONE (either) field terminal. The remaining field terminal goes to the remaining terminal on the regulator, (F).