M51A2 dump truck start system wiring help.

Just digging into a new to me non runner


Has the LDS-465-1A multi fuel engine.
I spent the long weekend downloading ALL the TMs and going through them looking for the wiring diagrams.
I only found one and that was for the early gasser which doesnt match.
Mine seems to be a later 60s perhaps? It was last painted carc in 2003 so possible it had some later retrofitting like a larger primary fuel filter and who knows what.
We got it from BIA so who knows what "field expedients" were applied to it.
The start button is missing and may have been replaced with this abomination...


It has what looks like a start relay but seems to be missing a voltage regulator



It has an unknown condition fuel lift pump in the left tank but without a wiring diagram to look at I am not sure where it draws power from or when .



The truck is at a remote storage lot in 114 degree heat and I was hoping to be able to research and understand it before I get into the oven.

Mainly looking for schematics of the starter/relay/lift pump/battery(master)switch/voltage regulator relationship

Looks like a good rescue!

spent about an hour today before the heat got to me. Tracing some wiring.
It has a 60 amp generator fitted with built in regulator so that explains the missing regulator from the fire wall.



The battery positive wire goes directly to the starter solenoid. A wire from the BATT stud goes up to the start relay box and another from the relay back down to the start lug of the solenoid. I dont see where the rest of the truck gets power from though.





I got the battery switch accessible and saw some wiring issues before giving in to the elements





Not sure what these two circuit breakers are for...

Wiring looks really bad. Suggest this needs to go home on a towbar, wrecker, RGN.

We had it transported by our go-to guy.




We are just at the "get it running' stage right now.
Topping fluids, Trying to get power to crank and cleaning the fuel system

I am also looking for the wiring diagram for this series truck. Only thing I have come up with is the gasser wiring diagram in TM 9-2320-211-20-2-2

I have one of these trucks . I don’t have wiring diagram . Do you have the switch / lever in dash that when in the on position it covers up the fuel shutoff pull handle ? This turns on the main power to the truck which turns on lift pump in tank . I would have to check and see if start push button is powered thru there also . I just had to
Remove my starter and clean contacts in solenoid. I have found a aftermarket solenoid on eBay by the way if needed . They don’t know it fits this starter but it does. I just had to change out the air valve on transfer case . It was leaking air real bad . Found nos one for $93 . Also changed the air valves on side transmission but it was not bad . Good luck with the brakes . I had to change out ever metal line . And Almosr every other brake part

the wiring to the battery switch.





These were the wires going to the battery switch.

According to a list if military "M-series truck circuit numbers" i found on the innerwebs...

#11 shows as "ignition"

#486 shows as "Manifold heater main engine"
#85 shows as "Low air pressure indicator light"

#24 shows as "light switch to blackout tail lamps"
#484 shows as "Turn indicator main blackout"

#87 shows as "spotlight circuit for trucks and wreckers"
#106 shows as "Gyro Cont to motor stab"
#38 shows as "Dome lamp circuit incl breaker and switch"

DREDnot said:

the wiring to the battery switch.

View attachment 950646

View attachment 950647

These were the wires going to the battery switch.

According to a list if military "M-series truck circuit numbers" i found on the innerwebs...

#11 shows as "ignition"

#486 shows as "Manifold heater main engine"
#85 shows as "Low air pressure indicator light"

#24 shows as "light switch to blackout tail lamps"
#484 shows as "Turn indicator main blackout"

#87 shows as "spotlight circuit for trucks and wreckers"
#106 shows as "Gyro Cont to motor stab"
#38 shows as "Dome lamp circuit incl breaker and switch"

Click to expand...

I’m trying to figure out the wiring for my battery switch. Can you tell on your which wires are in which spot on the battery switch? The switch will be labeled a,b,c and D. My truck is an a1 Mack so might be a little different but hopefully it’s the same as yours I do know I have two #11s that are hot.

The letters have deteriorated to where I cant positively ID which is which.

Plus the one wire that makes sense, #11 ignition, that has ribs on the connector, was not plugged into either of the two ribbed receptacles.
So i am skeptical as to the correctness of how they were hooked up.
I still havent found any wiring diagrams for this truck in this configuration

Here the trashed connector in the foreground was labeled 87/106/38. The dirty one to the left was labeled 486/85. Notice the position of the two ribbed receptacles.



Here is that wire 486/85 in the foreground and on the left is the frayed #11(ignition?) wire with a ribbed connector that is NOT in a ribbed receptacle which is concerning to me

DREDnot said:

View attachment 950726
Here the trashed connector in the foreground was labeled 87/106/38. The dirty one to the left was labeled 486/85. Notice the position of the two ribbed receptacles.

View attachment 950727

Here is that wire 486/85 in the foreground and on the left is the frayed #11(ignition?) wire with a ribbed connector that is NOT in a ribbed receptacle which is concerning to me

Click to expand...

Ok here is what I found out with mine today. You have 2 number 11s going to the switch. The ribs don’t match up on mine ether. One goes in d that feeds b and one goes in A and feeds C.Then you should have a wire 85/488, 85 is the air warning and I’m guessing 488 is the starter relay because with only that wire plugged in the air buzzer works and truck cranks. So I have the plugged into B. My fourth wire is marked 108/96/598/4 and I’m not sure what they feed yet but I have that plugged into A.

Good info. Thanks!
Where do the two #11s get power from? Do they terminate somewhere or do they go to a wrapped spice in the harness somewhere?
I have a significant short (thats melting my negative post) somewhere i need to find before I can hook up the batteries even.

DREDnot said:

Good info. Thanks!
Where do the two #11s get power from? Do they terminate somewhere or do they go to a wrapped spice in the harness somewhere?
I have a significant short (thats melting my negative post) somewhere i need to find before I can hook up the batteries even.

Click to expand...

are your sure you have battery’s hooked up correct . Disconnect the slave / jumpstart cables for now .

The batteries are hooked up properly. I will disconnect the slave receptacle though before proceeding.
We installed a new cable from the positive stud to the starter. A new cable between the batteries. The negative cable to frame was in good shape.
Four new clamps.





this is how the starter was hooked up. I took the pic BEFORE i had finished tightening the nut. Red taped wire in big stud goes to starter relay. the far wire comes from the starter relay. the foreground black wire goes to negative/ground stud on end of starter

Looking at your batteries mine has a smaller + wire hooked at the + 24 volt terminal . I would have to track where it goes . Maybe the generator ? Have you been able to spin the truck over with starter or no because of the positive grounding to frame ? I just had my starter apart to clean the contacts inside . Another one had on bench the contractor on top had all fell apart . Maybe this issue could be where yours is ground out ? Just a thought . I did find solenoid off eBay if Need I can tell you part number.

Have you tested the starter out of the truck ? Just curious

My truck is at my property out in the woods so can’t look at it till I go back out there .