MVT 1083A1 Battery Swap-out Power Problem

[jaws4518]

Guy's I'm newbie owner of a (MTV) 1083A1. That is what the data plate has on it. I am in the process of learning all about this truck. I acquired it from a VFD. They went from a 4 battery configuration to a 2 battery config. They disconnected the NATO slave receptacle and it looks like the 12V positive cable is not being used because it have electrical tape on the end. I assume that is 12V lead. Everything was working until I removed batteries yesterday to replace with new ones. Stupidly, I did not make note of which cable goes to positive side on one battery, and the other to the negative side on the other battery? One is short, the other is long coming into the battery box.

So, I have no power to the PDP when I flip the dash power switch. I assume that I created a reverse polarity situation and flipped a circuit breaker or something? I was reading that there is no way things will work without the 12 volt side of things being operational. So this cable that is taped off is probably not the 12V positive?

I was experiencing battery drain or a bad battery, so that is why decided to replace the batteries. I think the VFD guys were having problems after they changed the 4 battery configuration. I'm just trying to get back to a working situation where I can identify and correct. Just now, I believe I found the (2) battery configuration diagram. What I am starting to learn about the MTV/LMTV's is that there are too many variations in circuitry. This truck does not have the circuit breaker equipment at the battery box.

I'm sure this has been discussed time after time here, but I'm still looking for those posts. I see some MTVR conversations etc... If the new batteries continue to drain after I get back up and running, then I've got to trace that problem. Any recommendations or comments would be appreciated. -jw

 

[Keith Knight]

Do a continuity test from the PDP to the battery box on both the 12 and 24 volt.

 

[Ronmar]

OK, so it is an A1 without the disconnect switches to the rear of the battery box? Green circuit card power panel in the pax dash?

Not counting NATO plug wires, you probably have 4 large battery cables. Ground, 12 and 24v and a 24v line to the starter solenoid. Use an ohm meter and a long lead to positively ID them over to those same 3 connections on the alternator and one on the starter SOLENOID. IE: hook one meter lead to the 24 terminal at the alt and measure to the 4 cables in the batt box until you find the one that has the low resistance circuit. then do the one large cable from the solenoid. LABEL THEM AS YOU IDENTIFY THEM!

The large ground cable actually runs to the front of the starter motor CASE and a braided ground strap from there to the drivers frame provides ground return for the rest of the truck power.

Ground connects to - on the first battery(0-12v batt).
+ on first battery connects to - on the second battery(12-24v batt) using a short jumper cable. 12V connects to either of these two points.
The two +24V cables connect to + on the second battery...

 

[jaws4518]

Do a continuity test from the PDP to the battery box on both the 12 and 24 volt.

I will do that and post the result. I believe I have a good diagram.

 

[jaws4518]

OK, so it is an A1 without the disconnect switches to the rear of the battery box? Green circuit card power panel in the pax dash?

Not counting NATO plug wires, you probably have 4 large battery cables. Ground, 12 and 24v and a 24v line to the starter solenoid. Use an ohm meter and a long lead to positively ID them over to those same 3 connections on the alternator and one on the starter SOLENOID. IE: hook one meter lead to the 24 terminal at the alt and measure to the 4 cables in the batt box until you find the one that has the low resistance circuit. then do the one large cable from the solenoid. LABEL THEM AS YOU IDENTIFY THEM!

The large ground cable actually runs to the front of the starter motor CASE and a braided ground strap from there to the drivers frame provides ground return for the rest of the truck power.

Ground connects to - on the first battery(0-12v batt).
+ on first battery connects to - on the second battery(12-24v batt) using a short jumper cable. 12V connects to either of these two points.
The two +24V cables connect to + on the second battery...

I'm going out now to do as you have explained. I have four cables but one was taped off and not in use when I purchased the truck. I will report back with results. Thank you! -jw

 

[jaws4518]

Okay, Thanks for all the help. To make a long story short everything is good now. The ABS light actually disappeared on the dash. Cables are marked and I know my 2 and 4 battery configurations on this truck. I made long test leads years ago when I did a M929A1 cab makeover which I will post the project when I have time. I have an brand new STE/ICE which I bought years ago that the prob kit came from. I've played around with the STE/ICE on the my 900 series trucks a little bit. I just haven't spent enough contiguous time with it to see how effective it really is. Anyway, that is another subject.

So, when I got this truck they had two batteries in it and were having some problems. I believe the VFD got lost in it and gave up. The LMTVs are too complicated for them and I can understand that. They are use to the 800/900 series trucks, and the cab doesn't work for them either. Thanks for the step-by-step diagnosis instructions. This is a solid truck and I have been blessed to get another great deal on something I really wasn't interested in at first. -jw

 

[Ronmar]

Cool
2 batts is a good thing as it does not overload the puny 50/50 alts they chose to put in these things...

Other than the computer interface on the A1/A1R trucks, the STE they chose for these vehicles does not appear to be al that useful, and most any competent tech will quickly outgrow it... Some of the individual parts may be useful, but can be acquired or fabricated cheaper IMO.

 

[jaws4518]

Cool
2 batts is a good thing as it does not overload the puny 50/50 alts they chose to put in these things...

Other than the computer interface on the A1/A1R trucks, the STE they chose for these vehicles does not appear to be al that useful, and most any competent tech will quickly outgrow it... Some of the individual parts may be useful, but can be acquired or fabricated cheaper IMO.

Yeah, I hear you on the STE/ICE. By the time I get the lid to the thing open we have already solved the problem. I guess the fittings in the tray are probably the most useful thing but I haven't used them either. It would be a good step-stool, or paint it red with a big alarm clock strapped to it. I better not say any more...

 

[jaws4518]

Cool
2 batts is a good thing as it does not overload the puny 50/50 alts they chose to put in these things...

Other than the computer interface on the A1/A1R trucks, the STE they chose for these vehicles does not appear to be al that useful, and most any competent tech will quickly outgrow it... Some of the individual parts may be useful, but can be acquired or fabricated cheaper IMO.

OK, so it is an A1 without the disconnect switches to the rear of the battery box? Green circuit card power panel in the pax dash?

Not counting NATO plug wires, you probably have 4 large battery cables. Ground, 12 and 24v and a 24v line to the starter solenoid. Use an ohm meter and a long lead to positively ID them over to those same 3 connections on the alternator and one on the starter SOLENOID. IE: hook one meter lead to the 24 terminal at the alt and measure to the 4 cables in the batt box until you find the one that has the low resistance circuit. then do the one large cable from the solenoid. LABEL THEM AS YOU IDENTIFY THEM!

The large ground cable actually runs to the front of the starter motor CASE and a braided ground strap from there to the drivers frame provides ground return for the rest of the truck power.

Ground connects to - on the first battery(0-12v batt).
+ on first battery connects to - on the second battery(12-24v batt) using a short jumper cable. 12V connects to either of these two points.
The two +24V cables connect to + on the second battery...

Just wanted to followup on some questions that were asked that I did not cover. My LMVT 1083A1 which is the basic model from what I can tell. No recovery winch on this unit. It has a 3126 engine. 330 Hp I think. That is what the label says on the valve cover. It seem to be in pretty good shape but like all the trucks I have purchased, they all needed front-to-back servicing. This one needs a full health checkup. I have engine cooling issues which I will ask about in a new post or related thread.