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I replaced the solid state voltage regulator some time back and did not polarize the generator. Is polarizing necessary? My volt gauge needle shows mid green on the gauge when running. When I turn on all of the lights and hook up the trailer, after a few miles, the needle starts to drop down to the yellow zone. If I turn off the head lights, the needle moves back up to the middle. Is this caused by not polarizing the gen or just too much load on the system? If I need to polarize, how do you get to the connections to do so?
BTW I use the slave cable recepticle and hook up a slave cable that I have wired into a float charger on a timer, when I park the truck.
Thanks,
CT

Polarization only sets the residual magnetism in the magnets in the generator so if you have any charging at all then you do not need to polarize. It is very rarely needed, usually only after a generator has sat for many, many years or after a complete rebuild of a generator. It sounds like maybe you have a dirty commutator or bad brushes. The lights should certainly not be too much of a load. Sounds like you are going to be getting into the generator.

Still 24v waterproof system?
Do you have the test adapter set?
Procedure is on page 255 of TM9-8030

Yes, still 24v waterproof system, no, don't have a test set.

rickf wrote:Polarization only sets the residual magnetism in the magnets in the generator so if you have any charging at all then you do not need to polarize. It is very rarely needed, usually only after a generator has sat for many, many years or after a complete rebuild of a generator. It sounds like maybe you have a dirty commutator or bad brushes. The lights should certainly not be too much of a load. Sounds like you are going to be getting into the generator.

Technically, polarization is in the windings, as there are no magnets in these generators. But agreed, polarization is usually only needed if the generator has been disconnected from the wiring harness.

Sounds like it's time to put an ammeter in the generator output, and see what it is pumping. As rickf noted, it could just be dirty brushes or commutator. TM 9-1825B (the Autolite manual, 1952 edition) will be helpful here.

The test set (NSN 4910-00-348-7600) is worth the money to have for diagnosing electrical problems. If you buy one, make sure that it has all five adapters, like this one: https://www.ebay.com/itm/US-Military-Ge ... SwpYdaijur. If it's missing the instructions, I have a scanned copy that I can send you.

Cav, if your genny is not putting out any amps and you suspect a bad armature, I have a growler and would be happy to test your armature, no charge.

Thanks guys, I just bought the test set that Elwood posted the ebay link to. I am in the process of acquiring a M151a2 and that will let me have time to sort out what may be wrong on the M37. I haven't checked but do you know if the test set will work on the MUTT also? Elwood, are you in Michigan? If so, where? I'm in the Cincinnati/Dayton area but came from Niles, Mi. I visit my brother there when I can.
CT

A growler, I remember one of those from auto shop and the gas station I worked at right out of high school. Tools from the past that still have a use. IIRC we used a hack saw blade with it.

Yes, an old hacksaw blade held over the armature windings while on the growler will vibrate over a short. An old piece of equipment, but still useful with these old generators and starters.

Cav, yes I'm from Michigan. Originally from Detroit, but moved up north many years ago. You might remember that I stopped by your place a few years ago and purchased that fording air cleaner shroud that you had listed in the buy/sell.

Ah, yes, I thought I recognized you. Thanks for your input. I downloaded the TM and I just got notice that the test connector kit is being shipped. It will be interesting to find out what's going on. The truck has run fine but it always has charged batteries and short runs so I really don't know what the gen is doing. My 151 will hopefully be here in a couple of weeks if not sooner and will be something new to play with. I am going to MVPA convention to look/scrounge for parts if I need them too.
CT

I have an under cutter and somewhere around here, a growler. I also have a lathe I use for polishing the com.

I have a lathe and a mill that I could undercut with but no growler. I will have to see what some testing comes up with to see if I need to pull it and tear into it. Thanks for the offer. Hopefully I can at least test it in a week or so.

Cav Trooper wrote:Ah, yes, I thought I recognized you. Thanks for your input. I downloaded the TM and I just got notice that the test connector kit is being shipped. It will be interesting to find out what's going on. The truck has run fine but it always has charged batteries and short runs so I really don't know what the gen is doing. My 151 will hopefully be here in a couple of weeks if not sooner and will be something new to play with. I am going to MVPA convention to look/scrounge for parts if I need them too.
CT

The short runs (and low rpms) don't help much with the gen output. But testing it is the only way to know for certain. If there's anything I can do to help with the diagnosis, just send me a PM.

Congrats on the M151. Your A2 has a similar 24v waterproof electrical system, with a sealed distributor, so I think that some of the adapters in that test set will work on it as well as the M37.

Just out of curiosity, have you checked the output with a real voltmeter when this is happening? The dash gauges are famous for poor readings. You may have nothing more than a bad gauge, Or a dirty ground on the dash.

Not yet.