Operating an M37 with improper battery cable installation

[Norb]

It appears this M37 was operated for quite a few years with 24v positive to ground and 24v negative to the starter which is opposite to the original design.

I'm looking for either documentation or a 24v system expert to return these battery connections back to original design without destroying the M37.

Common sense tells me that when this mistake occurred, it did not damage the M37 at that moment when it started. So, if I correct this mistake by reconnecting 24 positive to the starter and 24v negative to ground/frame, it should operate without any damage to the 24v electrical system.

I've got too much invested in this M37 to rely on common sense.

Here's another common sense approach: the military designed this feature into the M37 vehicles [along with other types] knowing that the majority of combatant-bound draftees have no prior knowledge or experience of automotive systems and mistakes are made. Though swapping battery cables is a one-off event, there's must be a contingency to return back to original design without destroying the vehicle.

So, no guessing: I'm seeking either documentation that specifically addresses improper battery cable installation or an experienced mechanic that mitigated this issue first hand.

[RonD2]

It appears this M37 was operated for quite a few years with 24v positive to ground and 24v negative to the starter which is opposite to the original design.

Hi Norb, and welcome to this forum!

Question --- because it's not clear to me from your post: does your M37 operate this way now --- today?
Or put another way: have you operated it wired for positive ground?

Just my 2 cents, but I doubt you'll find an Army manual that describes connecting or troubleshooting batteries that are installed any way other than intended by the Army and the designers (negative ground).

I think 1950's military 24V electrical systems are pretty robust and forgiving (except for dead shorts, naturally) because they're mainly analog components, not like modern electronics.

I think there's a few M37 owners in the forum.
Hope they'll help you out!

And there's a couple of M37 manuals in the downloads section if you need a copy.

the military designed this feature into the M37 vehicles [along with other types] knowing that the majority of combatant-bound draftees have no prior knowledge or experience of automotive systems and mistakes are made. Though swapping battery cables is a one-off event, there's must be a contingency to return back to original design without destroying the vehicle.

Yeah, there was.
It's called a Sergeant.
Hard to find now-a-days.
Good ones are worth their weight in gold.

Good luck!

[RonD2]

Hi Norb,
Thinking about your question more, and without knowing the history of your truck, or the answer to my questions if it operates today (starts, charges batteries, lights work, etc), it seems to me that if everything runs now with batteries at positive ground then all the components are good and there are no short circuits.

The job of reconnecting back to negative ground could be fairly simple (easier said than done) but would require a very careful and detailed inspection of the entire electrical system and wiring harness to make sure every wire and ground connection is according to the Army manual. Lots of multimeter checks before connecting batteries.

After starting, probably also have to re-flash the generator field.

I have no experience with the M37 and only limited experience with 24v military electrical systems (while on active duty USMC 1972-2001, aviation electronics maintenance).
My M38 was converted to 12V by the previous owner and as much as I'd like to run 24V, the components are too rare and expensive for my wallet at the moment.

No sense wondering what kind of mechanic would leave you in this boat.
Any idea how it got this way? Did somebody from the U.K. own it before you?

Good luck!

[wesk]

Norb,

Back in the day when I was a young kid (1950's) positive & negative 6 and 12 volts systems depended on the manufacturers. It was common to see both in the same driveway. A lot of old timers recall the Mopar brands, Plymouth, Dodge, Chrysler & Desoto as positive ground systems. from before WWII thru the very early 50's. Even though the Dodge M37 was built under Army contract calling for the standard Army 24V neg grd system there were still folks around quite used to the civvy Dodge which was pos grd back then. Reversed polarity seldom causes any serious damage to the old school heavy duty electrics. I have corrected dozens of erroneous polarity reversal when I was still a young high school kid working nights and weekends in the neighborhood Cities Service station. Most often the only challenge was re-polarizing the electeric motors (Yes Generators are basically electric motors).

If as I gather from your post that your M37 is stock military 24V and it has been running fine with the pos post grounded then most likely a simple repolarization of any electric motors is all that is needed to get her back to negative ground. As Ron mentioned a careful inspection of the entire system to insure it is all tidy, ship/shape and ready to roll is just as important. Finally do a little reading in a good generalized electrical systems manual to understand the proper methods used to re-polarize your motors correctly based on their make/model/brand and their internal wiring which relates usually to weather the unit is internally or externally grounded.

It will help us better to advise you further but first you must gives us the details of your current electrical system including make/model/part numbers of any electrical motors (generators/Alternators/starters etc.)

[Investig8]

Hello Norb,
I have owned an M-37 for a few years, and while I am not an expert, I found a forum with many, many M-37 owners with many years of experience with them. If not already done so, you should post the question to that forum also. I believe the URL for the site is g741.org

Good Luck,
Dennis

[wesk]

Good point, I have been a member of the G741 site for about 15 years. Ever since I bought my M37. I would offer him the same advice there.

Here's the link: http://www.g741.org/PHPBB/

[Norb]

I thank those that have replied to my issue [in other words, I found my way into this forum]. I have posted this same issue in the g741 site with the same results.
..
I tried to not throw money at this problem but that's what I have to do now.
..
I appreciate your feedback - it was worth the effort. I will not be signing back into this forum - the keepers can delete me from the roll-call list.