Mr1964cj5

[Mr1964cj5]

Can anyone help me out with a problem I have with my amp light staying on all the time. Had the generator overhauled along with a new voltage regulator. My amp light has a wire going to the ignition switch and one going to the voltage regulator. Any ideas out there?

[gmwillys]

One question, is the amp light staying on all the time, even with key off? If they amp light is wired into the hot side of the key switch. I don't have a schematic handy, but it is a basic set up. If the light stays on after the key is on, and the engine is running, check for a dirty or loose ground. Hope this helps a little.

[Mr1964cj5]

The light is only on when running. Not sure what the 2 wires hooked to the idiot light do as one goes to regulater and other to ignition switch. Only ground wire I see is the ground wire from regulater to starter case

[gmwillys]

Just want to make sure. I get myself into trouble making assumptions. Most time, the regulator grounds to one of the bottom mount bolts to the fender. After painting, it's tough to grind a ground in the fresh paint. If all checks out with the ground, then the regulator needs to be checked for battery voltage when the engine is off. You installed a new regulator, and a rebuilt generator, but was the polarity set after installation? I can not link a post to help, but it can be found on the net. Also full feild the generator to make it out the max voltage.

[Mr1964cj5]

I will check the ground again. Not sure what you mean full field the generator but I did do the polarity with the regulator. Not sure where to go from here

[LarrBeard]

Full fielding a generator is a term used to describe the process where you drive a bunch of current into the field coil to see just how much voltage the generator will produce. The voltage output of a generator is regulated by limiting the current going into the field coil.

There are a lot of ways to do this, but here is a way that is pretty safe and won't damage anything.

Go get a big square six-volt lantern battery - the kind with spring contacts.

You will need a couple of jumper leads to connect it to the generator. You are going to use this battery to provide current to the generator field coil to create a magnetic field in the generator. The lantern battery won't deliver enough current to damage anything. Connect the NEGATIVE terminal to the generator ground terminal.

Disconnect the field and armature leads from the generator. The ARMATURE is generally the larger of the two insulated terminals, the FIELD is the smaller. GROUND or NEGATIVE is the screw into the generator frame.

Connect a voltmeter to the armature terminal of the generator. If it's a manual voltmeter, set to read about 50-volts (you can adjust later). Start the vehicle (generator is turning). Connect the POSITIVE terminal of the battery to the generator's FIELD terminal.

You should get a significant voltage reading on the voltmeter. Vary engine speed and the voltage should vary - higher speed, higher voltage. Don't be surprised at 35 or more volts on a 12-volt system - that's why you disconnected the ARMATURE terminal on the generator; 35-volts doesn't do batteries or bulbs any good.

If you get the high voltage from the generator, you have pretty well proven that the generator is working.

I don't like to full field a generator using the vehicle battery because it can deliver LOTS of amps into the field coil. The lantern battery will current limit itself below damage level.

Don't run at the high voltage too long, just satisfy yourself that things work. It is not out of the question that the "new" voltage regulator is defective. We had a new regulator fail when we were doing the '48 (another oh-by-the-way) and we used this process to isolate whether the 70-year old generator or new regulator was the problem.

If the generator checks OK - I'd replace the regulator after I checked all of the wiring.

Let us know what you find.

[Mr1964cj5]

If you connect one lead of the volt meter to the armature then where do you connect the other lead?

[LarrBeard]

Sorry, my error in not giving complete instructions.

Positive voltmeter lead to ARMATURE, negative to vehicle ground - make sure you have a clean place, no paint or rust.

Let us know what you find....

(Then, you'll be an expert).

[Mr1964cj5]

Only other question is do I use 6 volt battery or 12 volt like the Jeep is

[LarrBeard]

The square lantern battery is a 6-volt battery. All it is doing is putting a couple of amps of current through the field coils. 6-volt battery is fine.

[Mr1964cj5]

Ok I will let you know. Thank you so much for your help

[LarrBeard]

In a private post - you wrote:

I used the 6 volt battery and tested generator. the volt meter reads voltage and as i increase engine speed it also increases voltage. Only thing is my Fluke meter shows negative number and wasnt sure it should. Everything is hooked up as it should. Please advise. Thanks

I'm going to repost this so everyone can learn from what we are trying to do here.

Interesting... that's a more professional way to say "What the heck is going on?"

A. The most common way that you would get a negative voltage out of the generator is to have the meter leads reversed. That is the simplest one to fix. The meter red lead goes to + (ARMATURE) , black to - (FRAME).

B. The next idea I have is that you have the field coils reversed. The positive terminal of that lantern battery is the one at the corner; the negative is the center spring. Make sure that you have the POSITIVE (corner) terminal connected to the FIELD terminal on the generator. If you got it backwards the first time, you swapped the North and South poles of the field pieces and, although I never have done this, it could swap polarity of the output from the ARMATURE. No problem - when you hook it up correctly, it will fix itself. Try again and make sure the corner spring (+) goes to the FIELD terminal, center spring (-) to the frame.

C. I don't see any way that the generator could be turning in the wrong direction ...

Let us know what you find - but even with a negative voltage I suspect you have a good generator. How many volts did you get when you spun it up?

[Mr1964cj5]

I double checked all my connections and had everything right. I started engine and I have around 12volts at idle and as I increase engine speed it goes up to 40 plus but meter still shows minus sign. I’m not sure why it’s showing negative voltage. So then I decided to check the meter and battery and with the leads hooked to battery I get 6 volts and on the positive sign so I guess that confirms that the problem is not in the meter. Not sure what direction I need to go now. Not sure this is telling you much.

[Mr1964cj5]

I was just giving this some thought and being that I just had this generator worked on and they put new fields in it is it possible to put them in wrong so as to run negative voltage?

[LarrBeard]

I was just giving this some thought and being that I just had this generator worked on and they put new fields in it is it possible to put them in wrong so as to run negative voltage?

Well, I'd take it back to the shop and have them run it on the test bench just to make sure things are right. The 12 volts and 40 volts sound like what I would expect (now you know why I suggest you take off the ARM terminal...