HMMWV M1097R1 Voltage/charging Issues

[Joe Wiater]

Hello everyone, my name is Joe Wiater and I am new to this forum.
I am 18 years old and recently purchased a HMMWV as a marketing standpoint for a night vision company my buddies and I started. I have a mechanical background with cars, I've worked on them since I was a little kid and understand the basics, I'd say. What led me to this forum is quite the story.

About a week ago I drove to pick up this HMMWV from Pennsylvania. The wait light turned on before starting then turned off like normal, the voltage was good, oil pressure was good, all the gauges worked, the windshield wipers worked, everything worked. I took a gamble and decided to make the trek back to my place in Michigan and thankfully made it, but barely. On the way home my windshield got very dirty with bugs, etc., and I decided to try the windshield washer system for kicks. I was trying to figure out how it worked, so I either pushed or pulled the windshield knob and every gauge in the truck went out. I panicked and either pulled or pushed the knob back in and everything was fine. We stopped at a rest stop and my friend bumped the knob this time, but instead my gauges remained the same except my voltage gauge dropped to the yellow. We frantically sat there trying to figure out how to reverse the issue but failed. It got to the point where we decided to just disconnect the windshield wiper cables entirely in case there was a short and continue back home, while the WAIT light was on this entire time. I was in panic mode the entire time, but eventually the voltage went back into the green, but the WAIT light was still on. It was night out so the truck made it all the way home with all of its lights on. We probably drove 4 hours with this issue.

We parked the truck and in the morning got in it to start it, and as we drove it around the voltage dropped back into the yellow and the WAIT light kicked back on. The voltage has been in the yellow ever since. I did some snooping around and didn’t notice anything out of the ordinary, all wires were connected and grounds looked clean. I pulled out the multimeter and came to the conclusion it probably needed a new voltage regulator. I did my research and from what I have read, it is almost never the alternator, apparently they were well built and rarely are issues. I placed an order for a new factory correct voltage regulator and installed it hoping it would fix the issue but it did not. I brought out my multimeter once again and here were the readings on the voltage regulator terminals.

When HMMWV was running:
14v+ terminal: 0.8v
IGN terminal: ranged from 2v to 14v and would constantly fluctuate without stopping (would maybe hold 9v for a couple seconds, even once saw 24v but extremely briefly)
AC terminal: 0.31v
Battery lead: 24.4v

When HMMWV was off:
14v+ terminal: 0.8v
IGN terminal: 0.6v
AC terminal: 0.5v
Battery lead: 25.3v (maybe because there was zero current draw that it increased a volt when it was off???)

This stumped me because to me this seems like a voltage regulator issue, but I just replaced it and it is from 2017 (although it was a surplus part and never tested, but the guy said it sat on a shelf for years). I tested both batteries individually and they were both good. I even went as far as taking 2 batteries out of my car that I knew were in good shape and installed them to see what happened, but still the voltage was in the yellow. What’s weird to me is how many times I drove and started the HMMWV and the batteries never died. This doesn’t make sense to me because it almost seems like they are charging, but it could just be running off of fumes. I can’t imagine it draws too much power when zero accessories are on, except the lights occasionally. After doing all of these tests I jumped the batteries to make sure they had enough charge so I could drive the HMMWV home from my shop. On my way home I noticed that if you turn the lights on and honk the horn the WAIT light goes off... WTH.

Does anyone know what the issue is? Maybe it’s an alternator issue? Maybe the "new" voltage regulator I got isn’t actually in working condition and it just so happens I have 2 faulty voltage regulators? Is there some way I can test the alternator or voltage regulator separately to determine which is the issue? could my guage be bad?

I am by no means a mechanic but I understand the basics and would appreciate help. I am a young adult just trying to have fun and grow my company.

 

[Coug]

Just to clarify, do you have a 3 speed truck or a 4 speed truck? Some 3 speed trucks have the 14V terminal on the 200 amp alternator wired to a ground point instead of the rear battery positive, so if that's the case then seeing 0V at it would be expected (not 0.8V, but sometimes weird readings happen?)

0.8V at the 14V tap leads me to believe you have either a bad wire or bad connection on that circuit. It should show the same voltage as the rear battery when running or off if it's wired to the battery.

IGN voltage fluctuating would lead me to believe that either your start box (sometimes smart, sometimes just idiotic) is failing internally, or you have a bad wire connection somewhere.

The fact that the wait light is also coming on and staying on also suggests a start box issue, or possible bad wiring.

If you don't get good voltage into the regulator at the ign terminal, you won't get good voltage out.



And just to clarify my first question, the M1097R1 trucks are recapitalized early variants upgraded to become heavy versions, and could either be 3 or 4 speed trucks depending on what they were before rebuild and redesignation.

 

[Joe Wiater]

Just to clarify, do you have a 3 speed truck or a 4 speed truck? Some 3 speed trucks have the 14V terminal on the 200 amp alternator wired to a ground point instead of the rear battery positive, so if that's the case then seeing 0V at it would be expected (not 0.8V, but sometimes weird readings happen?)

0.8V at the 14V tap leads me to believe you have either a bad wire or bad connection on that circuit. It should show the same voltage as the rear battery when running or off if it's wired to the battery.

IGN voltage fluctuating would lead me to believe that either your start box (sometimes smart, sometimes just idiotic) is failing internally, or you have a bad wire connection somewhere.

The fact that the wait light is also coming on and staying on also suggests a start box issue, or possible bad wiring.

If you don't get good voltage into the regulator at the ign terminal, you won't get good voltage out.



And just to clarify my first question, the M1097R1 trucks are recapitalized early variants upgraded to become heavy versions, and could either be 3 or 4 speed trucks depending on what they were before rebuild and redesignation.

I do have a 3-speed.

The 0.8v would make sense because sometimes my multimeter, if I have just recently tested something, will read about 0.5v when I’m not testing anything, so it probably has 0v. I will check the ground on the 14v terminal, I did not know that was a ground.

When you say the 14v tap should have the same voltage as the rear battery, you literally mean the furthest back 12v battery in the battery tray, correct?

I will check out the start box today and trace all of the wires to see if I can find anything.

 

[Coug]

I do have a 3-speed.

The 0.8v would make sense because sometimes my multimeter, if I have just recently tested something, will read about 0.5v when I’m not testing anything, so it probably has 0v. I will check the ground on the 14v terminal, I did not know that was a ground.

When you say the 14v tap should have the same voltage as the rear battery, you literally mean the furthest back 12v battery in the battery tray, correct?

I will check out the start box today and trace all of the wires to see if I can find anything.

The rear battery is the one wired with the negative terminal to the DC shunt on the side of the battery box, and yes, it is towards the rear of the vehicle (if the batteries are properly installed and wired according to the diagrams)

On some 3 speed trucks the 14V tap got wired directly to ground, on others it didn't get wired to anything; either way your batteries will be happier and live longer if you run it to the positive terminal of the rear battery (or whichever one is connected to the negative post of the other battery in the box; just not to the same post as the positive wire going to the starter)




Reading back through your post, first time you used the washer pump gauge went dead, second time voltage reading dropped) very much suggests the issue is in the wiring or start box. Start box is the common connection where power to both the gauges/washer/wiper system and power to the ign terminal on the alternator. It isn't terribly hard to remove and open up to take a look inside for burnt up componenets, but make sure you disconnect the batteries before you remove the plug on the start box.

While you are at it, you might also double check the bolts on the DC shunt in the battery box. One bolt goes through the box and on the opposite side is the ground wire for all vehicle power, and occasionally that bolt will be a little lose causing some electrical issues. I doubt this is the direct issue but might be related.


And to reemphasize, when you disconnect the smart box/start box, make sure you have the battery ground cable disconnected first, otherwise you definitely WILL have a start box issue even if you didn't before.

 

[Joe Wiater]

The rear battery is the one wired with the negative terminal to the DC shunt on the side of the battery box, and yes, it is towards the rear of the vehicle (if the batteries are properly installed and wired according to the diagrams)

On some 3 speed trucks the 14V tap got wired directly to ground, on others it didn't get wired to anything; either way your batteries will be happier and live longer if you run it to the positive terminal of the rear battery (or whichever one is connected to the negative post of the other battery in the box; just not to the same post as the positive wire going to the starter)




Reading back through your post, first time you used the washer pump gauge went dead, second time voltage reading dropped) very much suggests the issue is in the wiring or start box. Start box is the common connection where power to both the gauges/washer/wiper system and power to the ign terminal on the alternator. It isn't terribly hard to remove and open up to take a look inside for burnt up componenets, but make sure you disconnect the batteries before you remove the plug on the start box.

While you are at it, you might also double check the bolts on the DC shunt in the battery box. One bolt goes through the box and on the opposite side is the ground wire for all vehicle power, and occasionally that bolt will be a little lose causing some electrical issues. I doubt this is the direct issue but might be related.


And to reemphasize, when you disconnect the smart box/start box, make sure you have the battery ground cable disconnected first, otherwise you definitely WILL have a start box issue even if you didn't before.

Thank you, I will check this out later today

 

[Joe Wiater]

I traced the 14v cable on the voltage regulator and it led me here. it was loose, so i got my hopes up but after cleaning it off and tightening it down, it did not solve the issue. next step is the starter box.

View attachment tempImagebimQZU.jpg

 

[Coug]

14V tap won't affect anything in your truck. 3 Speeds trucks originally came with a 60 amp 24V only alternator, with nothing in the truck utilizing 12V.

Need to stop focusing on the alternator; your erratic voltage is a symptom of the issue, not the cause in and of itself.