LMTV Volt Gauge Readings

[Dexis]

Hey all, my LMTV volt gauge has what I'm thinking is an odd reading that I would like some input on. My Volt gauge on startup reads right where I would expect it to be.

As I drive around, currently only low speeds as a ranch/farm truck the volt gauge seems to continually drop, seemingly rapidly over a few minutes, down towards the “yellow”.

I just did the swap to a pair of group 31 batteries, about to switch to 27’s. (Didn’t like how much material was going to have to be removed to “properly” fit the 31’s so decided to go pair of 27’s instead.) Truck is running great but I notice the volt gauge seeming to slowly drop out.

I just had a good fight with the charging system over the past few weeks but everything on that front has been sorted out. Im mentioning that because through my testing I know at this point the volt reg and alt are operating normally now, but the volt gauge seems to keep dropping.

Im wondering what the likelyhood is that the Volt gauge is malfunctioning somehow vs an actual issue. Driving it on the ranch roads Im not running anything besides the aftermarket AC, no lights etc. Im wondering what the likelyhood iof this being an actual power issue vs the volt gauge reading off.

I havent yet hooked up a voltmeter while im driving and this is happening but its on the to do list. With the issues I had recently with the transmission over and under voltage problems ive been too traumatized to let it drop down into the yellow while out at pasture.

When I shut the truck down for a bit and fire it back up the Volt gauge jumps right back well into the green around the ~28V range.

Is this something anyone has run into before or is this charging system really so underpowered if you needed more than a dome light you’ll brick your truck?

 

[Ronmar]

Is the AC you are talking about DC powered, and if so what voltage?

have you gone thru the main ground straps, they are junk from manufacture With a layer of paint in the middle… strip them all to bare metal, throw away the star washer and re-assemble with dilectric grease or copperkote, then paint over them with spray paint or galve-coat spray.

starter to drivers frame
alt to passenger frame
cab tunnel to passenger frame (behind grill)
inside cab tunnel to far right passenger dash(near grab handle)
passenger dash to power panel ground test point which feeds TB2 where everything in the truck dash is grounded…

check all your connections between alt and batteries(alt, batteries and polarity protection device) . The alt/reg is not just an alternator it is a battery balancer, and it will not regulate properly and even de-rate(to 13/26v) if it does not see a properly reacting 12 and 24v from a series wired battery string.

yes it could be a gauge or dash wiring issue. On the A0 they actually put in test wires to monitor alternator voltage directly to the STE connector under the drivers dash. I repurposed those wires(24v and gnd) to monitor 12 and 24 at the alt to digital gauges in the dash. Until you alternately measure the voltage at the alt you won’t know. I suspect y0u are probably having connection issues(grounds or batts to alt)…

 

[Dexis]

Is the AC you are talking about DC powered, and if so what voltage?

have you gone thru the main ground straps, they are junk from manufacture With a layer of paint in the middle… strip them all to bare metal, throw away the star washer and re-assemble with dilectric grease or copperkote, then paint over them with spray paint or galve-coat spray.

starter to drivers frame
alt to passenger frame
cab tunnel to passenger frame (behind grill)
inside cab tunnel to far right passenger dash(near grab handle)
passenger dash to power panel ground test point which feeds TB2 where everything in the truck dash is grounded…

check all your connections between alt and batteries(alt, batteries and polarity protection device) . The alt/reg is not just an alternator it is a battery balancer, and it will not regulate properly and even de-rate(to 13/26v) if it does not see a properly reacting 12 and 24v from a series wired battery string.

yes it could be a gauge or dash wiring issue. On the A0 they actually put in test wires to monitor alternator voltage directly to the STE connector under the drivers dash. I repurposed those wires(24v and gnd) to monitor 12 and 24 at the alt to digital gauges in the dash. Until you alternately measure the voltage at the alt you won’t know. I suspect y0u are probably having connection issues(grounds or batts to alt)…

I have no idea on the AC system. Its the MME setup they sell. Tried to find any data to no avail. Already did alt/frame and cab/frame behind grill, but waiting on some dielectric grease before I tear apart any more ground straps in the harder to reach spots. Starter looks like a nightmare on the frame side, looks super buried under other lines/harnesses etc. Im tempted to just disconnect at starter and run a new strap off starter to an open area on the frame rail. Any issue cutting this corner here?

Also I pulled the lower plate off below fuse panel but cant seem to locate the ground there. Any photos available showing where I need to be searching? And as far as the ground that goes to the fuse panel, is pulling the handful of bolts that allow the fuse assembly to shift out a few inches the way to get to that?

Might be stupid questions but any info I can get on what to take apart where would go a long way for me. I already pulled alot of this apart once looking for a part that didnt exist so im learning to ask first lol.

 

[GeneralDisorder]

You remove the Phillips sheet metal screws above and to the back and on the front where the strip of sheet metal that the lid hooks to is mounted and the entire PDP pulls out on a wiring service loop. The military has specifications that require such service loops for maintenance accessibility.

You would know this procedure if you read the TM's. Go read the TM's like a good soldier, m-kay?

 

[Ronmar]

yep, if you are setting in the seat, the power panel should roll right out and lay upside down onto your knees, takes about 2 minutes to pull the top and bottom screws that hold it in the panel. I show this in one of my youtube videos for adding/repurposing the work light relay in an A0 into a 12V ignition relay. search username Rronmar to find my videos... the ground should run from tunnel to outboard edge of the panel out where the grab handle bolts on, and from there over to the ground test point on the panel...