Voltage regulator problem?

Sammy · Post by **Sammy** » Wed Jul 06, 2016 8:39 pm

Hello everyone.

Earlier this year I purchased my Grandfathers 1951 M38 (hood No. 2386078).

I got it running and drove it around the yard for a weekend, when I came back the next weekend I found my brother left the switch on and the battery's were dead, (oh well) so I charged the battery's and it wouldn't start. After some testing I found the new ignition coil had gong bad, so I changed the coil and spark plug wires and tested the voltage at the coil and got 28v. It has the 24v system.

My question is did I just get a bad ignition coil and 28-30v is normal or is there problem with the voltage regulator or something else and I will continue burning up coils till its fixed?

Thanks in advance.

Post by **wesk** » Wed Jul 06, 2016 11:54 pm

Sammy,

System nominal ratings are not the system charging rates. IE 6V systems charge at 7.5 Volts, 12 V systems charge at 14 Volts. So your 24 V systems charges at 28 Volts.

Make sure you get all the needed manuals for your new m38. Most are free on our downloads page.

The basics are:
TM 9-8012 Operator's manual
TM 9-1804A Engine & Clutch
TM 9-1804B Drivetrain & Body
ORD 9 SNL G-740 Parts Catalog

Nice to have are the system specific manuals:
TM 9-1825B (1952) AutoLite Electrical Systems
TM 9-8627 (1953) Delco Electrical Systems
TM 9-1826A (1952) Carter Carbs
TM 9-1828A (1952) AC & Carter Fuel Pumps
TM 9-1825E (1952) Bendix-Scintilla Electrical Equipment.

To pickup where the military manuals left off it is also nice to have the applicable CJ3A civilian manual SM-1002.

Back to your charging system, are you using a digital or analog VOM? To properly troubleshoot and adjust the regulator you will need an accurate digital VOM.

Before you tear into anything always start on these 50 plus year old jeeps with a good lookover for loose and or corroded electrical connections. Broken or missing ground straps. Pay particular attention to the ground strap at the right front engine mount. The cable shield that runs from the generator to the regulator provides the needed good ground between the two units. Make sure it's nuts are tight. Your normal voltage range during operation is 27.9 to 28.4 depending on ambient air temp. 30 plus volts will shorten the life of coils and lamps.

If you decide to work on the regulator settings again first a word of caution. 24Volts is extremely unforgiving!!!! A short will act like a welder very quick. Never remove /install the regulator cover with the batteries connected!!!!

Start with no electricity present and thoroughly clean the regulator interior. Use electrical contact spray cleaner and if needed file the contact points to remove and pitting and arc damage. Then clean it all and blow dry one last time.

Go to our downloads page and download the applicable portions of the AutoLite or delco TM you will need for the adjustment. Follow it exactly, step by step.

On another note, heat is another enemy of coils and if your military distributor does not have the vent lines attached, clear and good vacuum applied then that will also cost you short coil life.

Kendall · Post by **Kendall** » Thu Jul 07, 2016 7:02 am

Also, won't leaving the ignition switch on for extended periods of time fry a coil?

Post by **wesk** » Thu Jul 07, 2016 8:37 am

Yes if the points are closed.

Sammy · Post by **Sammy** » Thu Jul 07, 2016 9:48 pm

Thanks for the information, I'll look up the manuals. By VOM do you mean a volt/ohm meter? If so I've been using a nice digital meter.

We've checked the engine ground.

So this weekend I'll clean the regulator, air lines and a few other things.

Post by **wesk** » Thu Jul 07, 2016 9:58 pm

By VOM do you mean a volt/ohm meter?

Yes.