m923A2 Electrical issue

[Arizonacody]

Hello guys. My first time posting an I’m new to the 5ton truck. I got this rig an put a stockrack on it for hauling cattle out of the back country.

My issue is: after replacing the pcb an the alternator. As well as new battery’s. When I cycle the battery switch my gauges don’t come on. And when you go to engage the starter it won’t start from inside the cab, Bypassing the fsc, and turning the switches to the on position I can jump the starter from the outside and the truck will stay running I tested wire 459 at control box with battery switch turned on and there’s no power.
I’m told that wire 81a should always have power at the ignition switch but it is reading dead and wire 569 At the ignition switch I’m told is supposed to read 12 V but is currently reading 26.9, Based off the information I figured out is it safe to say that new battery and ignition switches should cure of my problem? Any input and advice is much appreciated

 

[simp5782]

What do you have power at the pins coming out of the pcb. List pin # or wire # and voltage

 

[Arizonacody]

What do you have power at the pins coming out of the pcb. List pin # or wire # and voltage

Pin 81 reads good, how ever 81a at the switch I have no power. Wondering where it ties into. I ran a jumper wire from switch to the starter an all gauges came on an truck fired up.

 

[simp5782]

Pin 81 reads good, how ever 81a at the switch I have no power. Wondering where it ties into. I ran a jumper wire from switch to the starter an all gauges came on an truck fired up.

Pin C at the pcb is wire 81. Should be 24v at all time. 81a branches off in the fat part of the harness behind the pcb. 459 with the key on should have 24v with switch on. 569 should be 12v if it is hooked up in the battery box correctly. It should be to 12v.


Do your lights work with the switch off?
81 meets 81a behind the pcb. It also meets 15 in there which is the power for the lights.

You may have to just cut 81a and isolate it and run a new wire. You can run a new 81 wire as well to the pcb but you would need to tie the 15 in as well.

 

[Arizonacody]

Pin C at the pcb is wire 81. Should be 24v at all time. 81a branches off in the fat part of the harness behind the pcb. 459 with the key on should have 24v with switch on. 569 should be 12v if it is hooked up in the battery box correctly. It should be to 12v.


Do your lights work with the switch off?
81 meets 81a behind the pcb. It also meets 15 in there which is the power for the lights.

You may have to just cut 81a and isolate it and run a new wire. You can run a new 81 wire as well to the pcb but you would need to tie the 15 in as well.

After all day peeling tape back I traced 81 a back behind the pcb box an found where it had shorted out an burnt back toward the starter. Tomorrow I’ll replace it an hope to have power back to the switch as well as you mentioned to the lights. I appreciate your help sir

 

[simp5782]

After all day peeling tape back I traced 81 a back behind the pcb box an found where it had shorted out an burnt back toward the starter. Tomorrow I’ll replace it an hope to have power back to the switch as well as you mentioned to the lights. I appreciate your help sir

Be sure to cut the tape off. Use mineral spirits to clean harness free of tape goop. Then rewrap with tape. Or asphalt loom covering it you can source it that big. Usually not an easy find on the weekend and depending on your location

 

[Arizonacody]

Be sure to cut the tape off. Use mineral spirits to clean harness free of tape goop. Then rewrap with tape. Or asphalt loom covering it you can source it that big. Usually not an easy find on the weekend and depending on your location

Thank you for your help sir

 

[simp5782]

Thank you for your help sir

You're welcome

Please download the parts spreadsheet for your 5 ton since you are new here.

5 Ton Parts List- copywrited 2021

Sheet1 r,VENDOR,PART #,VENDOR,PART #,VENDOR,PART # M939A2 & M915 PARTS AT THE BOTTOM OF THE PAGE SYSTEM CAPACITIES Cooling System Capacity M939A0/1 w/ NHC250 Oil Capacity w/ Filter (w/o filter),27 Qts (23 qts) M939A2 Oil Capacity w/ Filter (w/o filter),20 Qts (18 qts) Allison Fluid Capacity Dry...

docs.google.com