LMTV M1078A1R - Battery Disconnect Reset Issue

[Third From Texas]

Ground under the power panel?

Is it in the kick panel or literally under the power distribution panel?

So much limited info on the A1R trucks it's a bit frustrating.

 

[Third From Texas]

So I started with the batteries one last time. Dropped in a set of 13v+ bats that had been charged last week and still holding full.

The "click" I can hear is confirmed as coming from under the cab/driver side (assuming that is the starter relay). The starter relay is mounted just above the frame rail. Jumping it only makes a spark (ign "on" or "off").

So before I start tearing into the cab electrical, any thoughts ?

I've tested most of the relays in the dash power panel (will have to pull and test the last bunch tomorrow). Electrical isn't my strong suit, but I'/m comfortable testing things with a good example. I wish I could find a full list of any/all ground straps on the A1R. I'm only checking the ones I can see between battery > starter > cab > alt but I know others exist.

 

[Suprman]

Pull up the relay panel. There is a grouped ground right side on a bolt that goes into one of the dash side grab handles. Sand and make good ground and put back together. The main truck ground goes thru a shunt up by the polarity box. So military diagnostics can measure current draw. Poor design though. Run a big ground wire fron the batts negative to a sanded spot on the main frame rail.

 

[Ronmar]

Well all the cab electricals work to make that aux starter relay click, so they are most likley OK. Now jumping across the contacts of the aux starter relay(circled in red) should cause the starter to crank the engine as it sends +24 to the starter solenoid.

 

[coachgeo]

maybe whack on the starter with a hammer... same with solenoid to see if possibly some crud has froze up just enough to lock some things in place??
At this point it can't hurt unless you start using hammer to take out all your frustrations. Granted that might help you though

 

[Third From Texas]

maybe whack on the starter with a hammer... same with solenoid to see if possibly some crud has froze up just enough to lock some things in place??
At this point it can't hurt unless you start using hammer to take out all your frustrations. Granted that might help you though

Did that with a ball peen hammer at the get-go three weeks ago.

After chasing every possible relay and ground, I fucked up went with replacing the batteries (well, I re-configured from quad to dual bats). Since they were showing 12.3v on all four, and the dash gauges were reading 11v and 22v to the dash from the CAT computer I figured it *might* actually be the batteries. Granted, if $500 later, my "special order" NAPA batteries arrived. Didn't resolve the issue.

Was tapping the starter relays and that again did nothing. Got the fucking sledge out and smacked the starter a couple of really good wacks. It started...

Now I'm out $500 for a pair of batts that are 12.9v (but I can also start it fine with either pair of the old 12.3v batteries ).

Sucks because that's about two solid months of my project funds (disabled and living small).

/sigh

 

[Third From Texas]

I'm concluding your info is for the earlier generation A1 trucks with the CAT 3126 up to 2005. The truck I have is 2006 which has the CAT C7 and WEC 4/5 so it's a complete different setup. I do have a digital copy of the early A1 generation TM's but they've been no help on the issue due to the changes they made. Here's photos of the PDP for comparison for A1 trucks. The only other A1 PDP would for the rebuilt Oshkosh units but we'll get to that when Uncle Sam is tired of playing with those toys.

A1 w/ 3126 (Early Gen)
View attachment 774964

A1 w/ C7 (Later Gen)
View attachment 774965

Yes, I have an A1R with the C7

 

[Third From Texas]

Btw:

The "click" was coming from the small relay just above the upper frame rail.

I have to assume that is the "remote starter relay"?

There are clearly the two hots (heavy gauge with red covers) and the two black wires (top and bottom).

In any event, it was beating on the starter that got me running (for now, I will have to look into rebuilding or replacing the starter asap).

 

[coachgeo]

when all else fails....... get a bigger hammer

glad it worked for you. Your starter may just need cleaning.

 

[Master SPC]

I have a 2006 M1078A1R that is having an odd issue related to the battery disconnect box. This truck is current gen so no TM help. Batteries are fresh, wired correctly, and voltages checked. Turning the battery disconnect to "on" will result in a satisfying click for power. This click sounds like my other two M1078A1R trucks, nothing abnormal. The relay will eventually reset itself without a pattern or cause as shown by the video. Removing the cover and inspecting everything looks clean and almost factory new. I've had power to the dash at one point but now flipping the toggle switch for dash power gives me a second of power then causes the relay to trip and it resets randomly.

Has anyone had this issue? This would be good documentation as more of these trucks come out.

I'm currently Having this Issue now. what was the Main cause of the problem?

 

[fuzzytoaster]

I'm currently Having this Issue now. what was the Main cause of the problem?

Bad disconnect relay. Replaced or bypassed and all was good.

 

[LmtvPR]

First check I would make is that you are getting 12V and 24V power to X1 and X2 in the PDP. Then I would insure that the same power then passes on to X3 and X4 once the main sw is turned on.

The A1 did away with the dedicated crank lockout relay(k24 prevented starter engagement with oil pressure sw open/above 15psi). Instead it combined this function with the alternator excitation control. When you turn on the main sw relay K11 must energize to complete the circuit that allows the start switches to activate the start relay and crank the engine... Once the engine starts and the oil pressure sw opens at 15PSI, K11 de-energizes to disable the starter and excite the alternator...

This way actually makes more sense than the way they did it in the A0 as you can have a failed K11 and still start the truck, which will allow the alternator to try and come online while you are cranking the engine which can be very hard on the alternator/regulator...

I’m having a similar issue as above. Would you mind posting a pic or link of what the PDP x1 and X1 connections look like and where they are located?

 

[Ronmar]

I’m having a similar issue as above. Would you mind posting a pic or link of what the PDP x1 and X1 connections look like and where they are located?

Dont have a pic handy, on an A0 they are all the way over on the left edge of the compartment, three 1" diameter discs aligned vertically in the panel, for ground, 12 and 24v panel input from the polarity box. each has a threaded hole in the center...

On the A1 the panel has 4 boltheads spread out in the middle of the panel circuit board. two are for 12&24 input(batt) and two are for 12&24v from the ign relays located under the panel.

All these test points should be labeled on the panels...

 

[LmtvPR]

Dont have a pic handy, on an A0 they are all the way over on the left edge of the compartment, three 1" diameter discs aligned vertically in the panel, for ground, 12 and 24v panel input from the polarity box. each has a threaded hole in the center...

On the A1 the panel has 4 boltheads spread out in the middle of the panel circuit board. two are for 12&24 input(batt) and two are for 12&24v from the ign relays located under the panel.

All these test points should be labeled on the panels...

Ahh yes i know those thanks. I have a charging system light in my dash and only power sometimes when ignition switch is on and truck won’t start or crank and i can’t figure it out.