The Stovebolt Site Forums The Shop Area The Electrical Bay Ammeter puzzle

Had my cluster gauge rebuilt recently on my ‘47 AD Chev 3100 as the temperature gauge was broken. I carefully marked the wires, or so I thought, for the re-install.

When I installed the unit everything works EXCEPT the ammeter. When I start the truck, the ammeter constantly reads “ Charge” . When I turn the engine off ant turn on the lights, the gauge still reads Charge instead of discharge. I’ve tested the wires for continuity, the battery is new………..

Am I missing something? Did I cross a wire? Is there some other component-voltage regulator, generator a cause? I can’t seem to locate a short any.where. Is the ammeter fried? All gauges but the temp. Gauge worked before I removed the cluster.
I’m afraid I messed this up royally and can’t seem to sole this.
Has anyone faced a similar issue? What am I missing?

Your comments would be appreciated. Thanks

Could be as simple as you’ve crossed the wires at the ammeter. Try switching them and see what happens. If your generator isn’t working the gauge would show discharge with the ignition in or lights on. I don’t have a wiring diagram to confirm but think that would be correct.

Sounds like crossed wires at the ammeter to me as well.

I don't have a '47 wiring diagram, but I do have one for a '50 Chevrolet truck. Assuming the two are close to the same and that your wiring is stock .....

The + side of the ammeter should have two wires attached. One comes from the stud on the stomp starter switch. The other goes to one terminal on the horn.

The - side of the ammeter feeds the rest of the truck.


Do you KNOW the generator is charging when the engine is running? Quick test: Start the truck and let it idle with the headlights on at night. Have a helper rev the engine. Did the lights get brighter??

Bill is correct. The '47 wiring diagram is similar to the '50. His test of the generator works whether the ammeter is wired correctly or not.

Here's a LINK to the '47 wiring diagram.

Haven’t had a chance to try your suggestions. Saturday I will. The ammeter showed “charge” even when I turned on the lights. No needle movement at all toward discharge. That is confusing me. Never checked for high rev and increased brightness.
Will try both.

Just thinking….would this have anything to do with the polarity of the generator????

Does the ammeter center up (show neither charge or discharge) when everything is off? If so, that pretty much confirms you have it wired backwards.

You mention that the ammeter "constantly reads charge" when you start the engine. Does it continue to read charge even after the battery is fully charged back up?

If it does not settle to center once the battery is charged, it seems like you have the wire from the battery and the wire to the light switch connected to the wrong ammeter terminals. Just switch those two on the ammeter and see if that fixes the problem. Leave the wire from your regulator connected as you have it.

Mark

Don't do this. You'll end up with some of the load going through the ammeter and some not.

As Kevin and I said above, the + terminal on the ammeter gets the hot wire from the starter stomp switch and the hot wire to the horn. ALL OTHER WIRES CONNECT TO THE - SIDE OF THE AMMETER (assuming a stock electrical system).

Your points are helpful. My son has been helping and is far more electrically minded than me. Some things have been a challenge due to my inadequate knowledge.
Just to clarify, there is no marking for “+” or “-“ on the ammeter. Does the “-“ charge correspond to the Discharge post on the ammeter? With that, we should get things right.

I believe that is correct.

A portion of the '47 wiring diagram showing only 4 wires connected to the ammeter is shown below. COLORS ARE MINE IN THE DRAWING AND DO NOT REPRESENT ACTUAL WIRE COLORS.

Red is power from the battery via the stomp starter switch connecting to ammeter + side.
Also connected to the ammeter + side is the horn wire marked in blue.

The ammeter - side purple feeds the light switch.
Also connected to the ammeter - side is the "everything else" wire.

"Your mileage may vary" in the 77 years since the truck was new.

Got everything working with your suggestions.

The glitch I have is it still always charges...even after switching wires. Will check battery charge, generator output and the volt. reg. It seems mine could be a foreign made unit......and faulty. By process of elimination, I will uncover the gremlin!

Thanks again for your help.

We swappped the ammeter wires...positive and negative. The ammeter still reads the same....Charge. At idle we are about 6.1 V at the battery. When we give it gas the voltage measures about 7 V at the battery for as long as we give it gas.

I’m suspecting the ammeter is faulty. Do yo agree with that conclusion?

Also when continuing to give it gas, are we getting into a serious overcharge situation?

7 volts would not be an overcharge situation on a 6V system. I drove my truck about 50 miles yesterday and I had swapped the ammeter wires because the previous drive showed discharge at highway speeds and charge when first turning the key on. The ammeter now shows charge, about 1/2 way to full charge at speed, although I have not measured charging voltage.
My new battery (1 day old) was dead halfway thru the drive after a stop (brake return spring doesn't shut off the brake lights), but I think I may need to look at the voltage regulator, which might not be disconnecting the battery when stopped.

Normal voltage against a fully charged battery on a "6V" system should be 7.5 volts while running. That will produce a 5-8 amp current going into a good condition 6V battery. Send me a PM and I can detail the proper way to check and adjust a mechanical contact regulator. It's a bit too complex of a procedure to do in an open forum post- - - -a phone call will be a lot more effective. I have a sneaky suspicion that the wiring connections at your ammeter are the cause of the problem.
Jerry