Fmtv no more dual voltage

[Ronmar]

If you are missing the other smaller device in the above pic that Ohiobenz posted, that is an instrunment shunt, used to measure current flow. It is placed in the main ground line between battery and starter and can measure crank current and total alternator output back into the batteries. The two large leads that attach to it can simply be connected together and insulated…

 

[GeneralDisorder]

What year is the M1079 you are picking up? It could use either a PPD (polarity protection device) or an LBCD (load battery control device).

 

[astacey1403]

HMU three 3 oh 3 three ate ate six too 5

Yup that picture you sent is definitely what is missing the smaller bridge is there but that larger PPD is missing. ( sorry i am not following the HMU and number set you listed in this message )

 

[astacey1403]

What year is the M1079 you are picking up? It could use either a PPD (polarity protection device) or an LBCD (load battery control device).

1998 M1079

 

[astacey1403]

Yea, that is the polarity protection box. It is just a set of diodes that prevents batteries that are connected backwards from doing damage in the cab. To get you off the lot, it can be bypassed, just don’t hook up your batteries backwards.

In the attached pic, connect the wires circled in red together(12v batt, alternator and load to cab) and insulate the connection. Then repeat the process for the wires in the green circle.

View attachment 868480

This diagram helps out a bunch. I figured I could bypass the system just was not sure. I will be attempting this when I go back to work on the truck. When I first went out to work on the truck I only had 2 new batteries with me in hoping that the truck only needed the 24v system to start but I do not think this is the case. I think the ignition system is a 12v energized solenoid for 24v starting. I had some members of this forum help me get the truck moved to an RV storage lot for the time being.

 

[Ronmar]

Most everything except the lighting is 24V, but the main ignition switch uses 12V to energize the control power relay (K02) that powers all the 24V circuits… Here is an abbreviated start circuit diagram I condensed from the A0 tech manual. You might need this When it comes time to start it

Probably should start a new discussion on any further adventures, as we just hijacked the heck out of this one… Good Luck

 

[Ohiobenz]

Yup that picture you sent is definitely what is missing the smaller bridge is there but that larger PPD is missing. ( sorry i am not following the HMU and number set you listed in this message )

Hit Me Up...

Its my phone phonetically lol - stops bots from reading it.
Follow Ronmar's instructions on connecting your cables.
If you can give me a call on the 2 parts i can ship pretty quick, they're no use to me so reasonably priced.