HMMWV Battery Polarity Keeps Reversing?

[JLAINC]

I have a 1985 M1038 and my rear battery keeps reversing polarity for some reason. I've gone through 3 batteries now, and I can't figure out what is causing it. I've recently replaced my generator and starter solenoid. Both since this happened the first time. It will be fine for a month or so, and then one day it will just not turn over good, and I check the batteries to find the rear one has reversed. Any ideas?

 

[BLK HMMWV]

How are you checking them.
Are they disconnected from each other as well as the vehicle?
This makes no sense

 

[86humv]

Its probably the PCB, or EESS box under dash.......Never seen a battery reverse.

 

[JLAINC]

How are you checking them.
Are they disconnected from each other as well as the vehicle?
This makes no sense

Both in connected, and out disconnected. No difference... I know it doesn't make sense, which is why I made the post!

With the first battery, I just chalked it up to a bad battery somehow...
With the second batter, I thought, hmmm...I wonder if my generator is causing this...
Then my generator when out, so I replaced it...
Now third battery post gen replace...

 

[Videris]

https://www.batterystuff.com/blog/battery-myth-can-a-battery-reverse-polarity.html

 

[JLAINC]

https://www.batterystuff.com/blog/battery-myth-can-a-battery-reverse-polarity.html

I know...I've already read this same text on another site. However, this has now happened 3 times on the same vehicle, same battery (rear) with 3 totally brand new batteries each time! It is happening WITHOUT any recharge occurrence. So...although this, "Just can't happen"... It HAS happened 3 times now in the last year.

 

[JLAINC]

One thing I failed to mention earlier on this post is that the rear battery which keeps doing this is running some 12V accessories, like an inline fuel pump, and some interior LED lights. These items are controlled by toggle switches mounted on the dash. I noticed the last time I drove it that the inline fuse was blown on the 12V connection, and the same fuse was again blown tonight. Hope that helps add some light on the subject!

 

[Videris]

Did the polarity problem exist before you added all these 12v accessories?

 

[gimpyrobb]

Did the polarity problem exist before you added all these 12v accessories?

That was my first thought. Put the truck back to stock and see if it happens.

 

[WILDBOY6X6]

I think your added lights etc may be the problem, we added a LOT of lights to a M998 here but ran them off of a 24 to 12 inverter hooked up to both batteries.
Some lights can be run on 12, or 24 by just changing the fuse to a 24v one, I would look at that idea because running stuff off of 1 battery will cause what you are getting.
The reason why is that the generator is trying to charge (by way of the PCB) the battery with your stuff on it more than the other one causing it to be over charged and fail.

 

[BLK HMMWV]

well that adds more info. Yes your problem most likely lies in all the 12volt stuff .
It is not recommended to tap 12 volts off of just one battery in a HMMWV.
The newer trucks have dual voltage generators on them with a 14 volt tap to allow for 12v loads.
Either change out the generator to a dual voltage one or find a 24 volt to 12 volt inverter.
For now I'd remove all the 12 volt gadgets and see if your problem goes away.

 

[JLAINC]

I think you might be right! This didn't start happening until I added the 12V inline fuel pump. I think the LED's will run on 24V with no problem, but I will have to get an inverter for the fuel pump anyway. Thanks!

 

[BLK HMMWV]

Ok now I have to ask why an in line electric fuel pump?
and why a 12 volt one at that.

 

[JLAINC]

Ok now I have to ask why an in line electric fuel pump?
and why a 12 volt one at that.

It is acting as a "Lift Pump" to get a fuel feed up to the filter, and the mechanical pump takes it from there. Instead of buying a 24v I just went to the local auto parts store and purchased an off the shelf 12v diesel pump. My truck was stranded, so I was in a hurry...

 

[porkysplace]

It is acting as a "Lift Pump" to get a fuel feed up to the filter, and the mechanical pump takes it from there. Instead of buying a 24v I just went to the local auto parts store and purchased an off the shelf 12v diesel pump. My truck was stranded, so I was in a hurry...

Sounds like the 12v pump was a band-aid and now it is time to fix it correctly , as it is creating new problems.

 

[JLAINC]

Sounds like the 12v pump was a band-aid and now it is time to fix it correctly , as it is creating new problems.

Right... I'm having a difficult time finding a 24V pump locally. Any suggestions?

 

[Retiredwarhorses]

Right... I'm having a difficult time finding a 24V pump locally. Any suggestions?

hmmwv's don't have electric lift pumps, I'm not understanding why you think yours needs something that's not on hundreds of thousands of the same vehicle, as well as god knows how many GM vehicles.....the mechanical fuel pump.
even if your fuel pump fails, your IJ pump has enough suction to draw from the tank and run...

 

[patracy]

I'm still confused, what's the need for the electric fuel pump? Is the mechanical pump not working?

 

[wheelspinner]

Sounds like it just needed to be primed correctly ? Did you run it out of fuel or change the filter when you became stranded?

 

[JLAINC]

Sounds like it just needed to be primed correctly ? Did you run it out of fuel or change the filter when you became stranded?

It would stall at high RPM's over a 30-60 second duration. I would have to sit at idle to allow the fuel supply to catch up before I could run again. Then eventually it would not crank due to lack of fuel. I have replaced both the mechanical pump and the injector pump, but still have the same problem. I even switched to a hi-flow Racor fuel filter, but without the inline pump to prime the filter it still has issues. I have actually seen where this is a pretty common mod for the HMMWV's. Here is a video: https://www.youtube.com/watch?v=Tk-cFvOHqJI