FMTV Battery hook up diagram

[Uberlandwerks]

Thank you, The photo was not appearing earlier today. Thanks again.

 

[sarge351]

Here you go. from a M1078. I recommend printing and taping inside your battery cover.

NOTE: this factory diagram is Misleading!!

Apparently there are two different kinds of Battery Diagrams:
1) With OUT Disconnect Switch
2) With Disconnect Switch

This is what I have on my truck (WithOUT). Apparently, it is missing, or not very clear, on a critical connection.

The BT2 (-) Terminal is supposed to connect to the 12 VDC Circuit, which enters the battery box on the left.

I put together an improved diagram, with the not very evident connection, highlighted in Yellow.

Without this BT2(-) to 12VDC Circuit connection, your Alternator will NOT work. I will add this diagram to the Alternator threads. This was the source of all my problems. I really had to hunt for this solution, because the battery connections are very poorly illustrated in the TM's, leading to a great deal of confusion.

 

[bikeman]

Apparently there are two different kinds of Battery Diagrams:
1) With OUT Disconnect Switch
2) With Disconnect Switch

Both Diagrams are in the first few posts of this page. With and without a disconnect switch.

 

[wheelspinner]

That is incorrect.

Here you go.

I just converted my 1078 to 2 batteries exactly as pictured. Everything seems to work just like it should. My question is why does it work right when the 12V+ is connected to the second battery Neg instead of the first batt +? It works but I don't understand WHY this is the correct hookup?

 

[Suprman]

Outermost terminals are negative. 12v is connected to the positive on the first batt which is also connected to the negative of the second battery. So you have the 12v from the first battery and then 24v from the two batts in series.

 

[joshua180422]

So my truck is stuck in the woods and my batteries are dead. Can you hook up this with just two batteries? If so how? It would come in handy because I️ leave my truck at my hunting cabin so I️ will be taking the batteries home with me every time to throw on the charger and to prevent theft.

 

[TNriverjet]

Yes, two batteries can work. You need one in the slot near the frame and one closest to you at the outside edge of the box. I had help from tnmogger and removed the two batteries closest to the cab. We left the remaining two in the rearmost slots. We protected the cable ends and did not remove any wires. The truck started, ran and charged fine on two batteries. I do not believe this is a long-term solution, but it can be done.

Please wear gloves and make sure your wrench doesn't contact the underside of the metal bed frame while loosening bolts! Also, you may want to look into a NOCO Genius G7200 charger. These are great charges and have a "repair" function. I was able to restore one of my two dead batteries. I replaced the DOA one with a NAPA 6TL. (Napa PN 7256)

 

[sarge351]

So my truck is stuck in the woods and my batteries are dead. Can you hook up this with just two batteries? If so how? It would come in handy because I️ leave my truck at my hunting cabin so I️ will be taking the batteries home with me every time to throw on the charger and to prevent theft.

I did a new diagram

Sent from my iPad using Tapatalk

 

[sarge351]

Here you go. from a M1078. I recommend printing and taping inside your battery cover.

NOTE: this factory diagram is Misleading!!

Apparently there are two different kinds of Battery Diagrams:
1) With OUT Disconnect Switch
2) With Disconnect Switch

This is what I have on my truck (WithOUT). Apparently, it is missing, or not very clear, on a critical connection.

The BT2 (-) Terminal is supposed to connect to the 12 VDC Circuit, which enters the battery box on the left.

I put together an improved diagram, with the not very evident connection, highlighted in Yellow.

Without this BT2(-) to 12VDC Circuit connection, your Alternator will NOT work. I will add this diagram to the Alternator threads. This was the source of all my problems. I really had to hunt for this solution, because the battery connections are very poorly illustrated in the TM's, leading to a great deal of confusion.

//uploads.tapatalk-cdn.com/20170529/11b81020ca1d589ab4c7f682fc4ca48b.png[/IMG[/QUOTE]

[IMG]//uploads.tapatalk-cdn.com/20171122/c7706161576fc44af848daaabaa5f731.jpg

Sent from my iPad using Tapatalk

 

[coachgeo]

If your hooking up two 12v chargers...... or two jumper batteries for purpose of getting her started after some stupid thing like leaving lights on.... where do you hook up when looking into the battery box on an A0

Then again lights are 12v.... guess the system is not really fully separated if leaving lights on can pull down the 24v side.

Anyway..... main question is mostly..... where to hook up to jump?


update..... found better thread for this question. See https://www.steelsoldiers.com/showthread.php?131264-M1078-jump-question

 

[HET CNC]

I’m in Plano too and today took an M1084 to my shop, batteries are dead and wouldn’t jump from a running HET(with bad batteries). I’d happily show you my HET for some advice on the M1084.!!

 

[Suprman]

With all of your batts dead, even with a 24v slave jump, you don’t always get the 12v to activate the relays.

 

[sarge351]

I’m in Plano too and today took an M1084 to my shop, batteries are dead and wouldn’t jump from a running HET(with bad batteries). I’d happily show you my HET for some advice on the M1084.!!

HET CNC - Send me a PM. I am in Allen, just next door. Would be good to compare notes.

 

[gslader]

I have a follow-up battery wiring question. In looking at the battery wiring diagram it all makes sense to with the exception of one connection, which I have circled in red below. From my understanding:
- BT1 & BT3 are wired in series for 24v and BT2 & BT4 are also wired in series for 24V
- (BT1 & BT3) are in parallel with (BT2 & Bt4)

Is the red circled wire effectively a load balancer that equalizes any differential across the two sets of batteries wired in series?

 

[Ronmar]

Well if you don't have it your 12v will consist of a single battery as you only have one 12v lead exiting the battery box. Without that jumper you can only connect that single lead to a single battery. With the struggle to keep the 12v side fully charged, this might not be a bad thing, will have to think on that one a bit…

 

[gslader]

Well if you don't have it your 12v will consist of a single battery as you only have one 12v lead exiting the battery box. Without that jumper you can only connect that single lead to a single battery. With the struggle to keep the 12v side fully charged, this might not be a bad thing, will have to think on that one a bit…

Got it! So that jumper effectively connects BT1 & BT2 in parallel at 12v. Makes sense now that you say it.

The 1078 that I just purchased was/is wired as shown in the following photo. It kind of twists my mind when I look at it but I guess it is just parallel in series versus the series in parallel that is suggested in the wiring diagram. So far haven't had issues with this wiring set-up but am in the process of replacing the batteries with 6TLs and will wire it as suggested in the wiring diagram.

 

[Ronmar]

BT3 & BT4 are the 12V batteries in parallel(voltage is referenced to ground). If your replacing batteries, I would highly recommend you drop to 2 batteries, especially if they are 6TL’s, and stay away from the AGMs… The 4 battery 6tl bank was gross milspec overkill and a terrible match for the 100A alternator… Cat specs a pair of Group 31’s for these engines… Wire them like the diagram Sarge351 posted a few posts above yours. Your alt will thank you, and the batteries will last a lot longer…

 

[fdrcva42]

I went to the truck today and I am starting to understand what you are saying.
The problem is I don't know which leads are positive and which leads are negative.
The only wires that are color coded seem to dead end at the NATO plug.

I am trying to lift the cab (hand pump) to trace things out but I have a nut that is leaking fluid hydraulic. It is a huge nut located between the cab and the bed. I tried to tighten it but it has a whole in the center that allows fluid to leak.

If you watch this video pause it at the 13 sec mark.....the nut in the middle of picture is leaking fluid. Sorry for the confusing description. How do I stop this from leaking so that I can raise the cab and get the battery wiring figured out.

Thanks

I put LUCAS stop leak on the seal surface, allow it to soak in and it stopped leaking a week later.