willysmjeeps.com

I've had my M38A1 over a year now, and the one thing I haven't had is battery problems. I swapped out the well used originals with two Optima yellow tops, and it's always been fine.
I went away for a week and a half. I came back tonight, went to start my M38A1, and it wouldn't start. The voltmeter didn't even register. I popped the battery lid off. The right battery (right with me at the engine facing the windshield) was a bit drained, but filled right back up with a battery charger. The left battery has white crusty powder on the two terminals, no voltage whatsoever, and when I try to charge it, the charger beeps until I switch poles. It will charge it in reverse apparently, but not the right way.

No sense chasing tails around the jeep. You obviously have a terminal corrosion issue which points towards a bit of overcharging by the generator/regulator. With a lot of raw acid on the top and sides of a battery it will allow the battery to leak down.

1-Remove the batteries.
2-Clean them and the box up with baking soda and flush well with water.
3-Drop the two batteries at the battery place or any shop that has a load tester and get them tested.
4-If they past the shop test, are recharged, then re-install them making sure all electrical circuits are turned off.
A-connect positive at driver's side.
B-Connect short interconnect cable to driver's battery Neg - and passenger's battery Pos +.
C-Connect a 24 volt test lamp to the unattached ground cable and the passenger battery Neg - post.
D- If lamp lites you have a current draw.
E- If the lamp does not light then you do not have a current draw.
5-Assuming there's no current draw connect the ground Neg- Cable to the passenger battery Neg - post.
6-Using the digital voltmeter with the red lead attached to the driver's battery Pos + post and the test meter's black lead to a good ground the pair of batteries should read 24 to 25 volts.
7-Start the engine and accelerate it to about 2500 RPM. The volt meter should now read 27 to 28.5 volts.

Tell us how your tests went to this point.

One of the batteries was bad, battery shop said it had a bad cell. I cleaned the box and the good battery, fully charged it, and put in a new one. Truck runs great now, thanks Wes

Just for sake of argument i thought the batts were to be changed out
in pairs. Perhaps that rule changed with modern batts??

No, that rule still applies to even modern batteries. I will assume the battery shop was not made aware that the batteries are used in series or they would have pointed that out to Dan.

Dan be sure to check out the alternator's charge rate. More than 28.5 and you'll just keep eating batteries. That 60 amp alternator you have has a simple adjusting screw.

The battery shop said just to make sure the other battery was fully charged, which I did. I have a generator, not an alternator, can I adjust it the same?

Post a photo of the generator you have and the regulator that should be on the passenger side frame rail alongside of the starter.

Sorry for the high contrast late at night photo, I can get a better one in the day if need be. This is the top of the generator. I don't have a regulator. I have a later packard style voltage gauge, and I could swear I remember being told I don't have a regulator with the high output generator/voltmeter combo. Or, at least I don't have an external one, it might be in the generator. I think John from Midwest was one guy who told me that.

That's a 60 amp 24V AC Generator better known as an Alternator. It has the regulator built in and is easily adjusted with the single voltage adjusting screw.

Adjust it as I said above if the charging voltage is not between 27.5 and 28.5 volts at 2500 RPM. Use a quality digital volt meter and take the reading as I stated above.

Ok, I'll do all that tomorrow. Where do I find the adjustment screw?

Pete Silfven has the manuals in PDF you can download at:
http://www.box.net/shared/hk9149dq15

Download both manuals and print them if you have a need to get the alternator worked on at your local shop.

I was planning on doing it myself. Do I turn the screw right or left (facing towards the front of the jeep) to increase the output?

Take another look at the top right corner of my photo. The black printing explains how to adjust and turn the screw.

I see it. Sorry.

It's 26.7 volts, 58.5 amps. Should I adjust it upward slightly?