The Stovebolt Site Forums The Shop Area The Electrical Bay 41 amp gauge

Got the 41 Gmc on the road ,3/4, and noticed as soon as I get going the amp gauge needle disappears into full charging land and does not drop down until I turn it off. The truck is still 6 volt, postive ground, the generator has been checked twice and the voltage regulator replaced and polarized, it has a new harness also. At idle the gauge has a slight charge, when I hit the lights it discharges, engine not running. Everything seems normal but it does not seem right for the needle to go off the scale. Am I overworring this?

If you turn the lights on with nothing running then you will show discharge. What happens when you turn on the lights at idle? discharge? At idle your not going to be putting out much amperage wise at all. when you increase rpms you should show increase in charge rate but not pegging out the needle. I would be worried about the full charge if in fact that is what it is doing. I would want to know how many amps you are putting out when you turn up the rpms and the needle goes all the way over. AMPS, not voltage. You may have to go to a local starter shop for this test. Typically I would say bad voltage regulator.....is it a good USA brand or made in India? I have seen generator armatures do funny things as well and that would be my next guess even though you have had it tested. I have listed a few things below that you can try. What about your battery? They can do some weird things as well and if you have another around that is charged swap them out and see what happens.


Here are some steps to take.
1. Check battery water and general battery condition to
see if it will take and hold a charge....Load testing
may be necessary.
2. Check wiring for damage and make sure all
connections at generator, regulator and battery are
tight and free of corrosion.
3. Make sure fan belt is tight enough to drive
generator at full capacity.
4. Run engine at medium speed. Using a wire, touch one
end to regulator base and other end to a good ground.
If this corrects trouble, regulator is not properly
grounded anymore.
5. If test 4 does not correct trouble, make this test.
Connect a wire from regulator terminal marked "ARM" or
"GEN" to regulator terminal marked "BAT" with engine
running at medium speed. If charging rate increases,
replace old regulator.
6. If test 5 does not correct trouble, make this test.
Connect a wire from "FLD" Terminal of regulator to a
good ground with engine running at medium speed. If
Charging rate increases, replace old regulator.

If none of the above test show a bad regulator then
there is probably a problem in the generator itself.

You don't really want to drive it like that. I would try disconnecting the field lead at the regulator and see if it still does it at higher RPMs. If it doesn't, you have a regulator problem. If it still does it, try disconnecting the field lead right at the generator.

battery is new and fully charged, new wiring harness, all other electrial items appears to be running ok. Will do your test and see what happens. As a side question what is the purpose of the fuse that is on the headlight switch? this is aGmc and it is the only fuse on the truck? do you know what size it should be? thanks Doug. P.S. when I say Pegged I mean totally of the charge side. This did this before I replaced the V.R. also?

The closest manual I have is for the 1939 Chevrolet truck. It has a fuse there which I believe protects all the light circuits including the headlights, tail lights, parking lights, dash lights and the dome light. It does not protect the ignition. I don't know the value yours would be but the 1938 sedan used a 15 amp fuse for this purpose.

What is the current flow when the gauge is pegged? Until you put an accurate ammeter in the circuit, all the hand-wringing over the dash gauge is wasted effort. It's entirely possible the generator is working right, and the gauge is lying to you. Testing a charging system without an ammeter is virtually impossible. A fully-charged 6V battery with a terminal voltage of approximately 7.5 volts supplied by the generator should be getting a charging current of about 7-10 amps, maximum. If it's flowing more current than that, the battery has internal resistance problems.

If you determinre that the battery is OK and the ammeter is the problem, you can reduce the current flowing through the gauge (and the needle deflection) by attaching a shunt to the back of the ammeter. Use a piece of stainless steel hose clamp material bent into a horseshoe shape, drill a hole in each end, and bolt it to the back of the gauge under the wires that are attached there. This will reduce the amount of current flowing through the ammeter by providing a paralell circuit, but the gauge will still register charge and discharge- - - -it just won't go full scale either way.
Jerry

I am going to get it tested asap, before I do anything else. You are right should know what current you got to start with. Doug