MTV grounding issue

SausageGuy

Member
102
13
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Location
Kansas City MO
So just got my M1084 together for the first time since auction. Starter, PPD, and batteries were all gone. Bought all new ones. Traced all wires down in TM and got hooked back up. Have voltages at PPD and alternator but nothing when I hit the power switch in cab unless I run a jumper cable from top of shunt to ground. Then it comes alive and everything works. Tried bypassing shunt nothing. Tried jumper to ground each shunt wire individually. With bottom one to ground got some dash activity but no crank. With top wire by itself nothing. With both to ground everything works. So I know shunt is fine. But still have a ground missing somewhere or corroded. Messed with alternator ground strap but didn't have enough mass in my ass to get it loose from frame. Will fire up air compressor and impact tomorrow. Any other ideas?

**also the jumper cable I added just goes from top wire of shunt next to PPD to bolt 12 inches above it. So it makes me believe ground to cab is good.
 
Last edited:

DREDnot

Active member
552
167
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Location
Phoenix, AZ
Ive just been educating myself on the wiring to help a friend fix his truck. I saw that there was a grounding wire behind the Power Distribution Panel...couldn't hurt to give it a look see.
 

Suprman

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Stratford/Connecticut
Main grounds meet at the starter. Wire goes into the cab bolts up under the power panel. The shunt under the spare tire? I think its just for diagnostic purposes. There is a cab to frame ground strap passenger side behind the front grille.
 

coachgeo

Well-known member
3,151
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Location
North of Cincy OH
Sure enough that ground wire is missing. I was wondering why the power steering res bracket was loose. I did not see it in TM either.
Its been said a few times that loose things.. Or things left undone is sometimes a purposeful hint from mechanics to auction buyer pointing toward problems. Sometimes its just they didn't feel was worth the effort to move forward on the fix.. Compared to replacing whole truck which was close to being replaced anyway.

So check out close and try to figure out their path so you can continue there journey,
 

SausageGuy

Member
102
13
18
Location
Kansas City MO
Yes I kind of knew what happened with this truck from auction pictures and it turned out to be true. The fuel filter and bracket was off the side of the motor and the starter was in the floorboard. I guessed they had lost prime and burned up starter trying to get it started then they started steeling parts off it. Sure enough fuel line from tank to motor was so brittle it just snapped if you bent it. Starter was bad. Put it back together with all new fuel lines and it fired right up.
 

Asymair95

Member
95
22
8
Location
Hudson Valley NY
I am chasing some intermittent electrical issues also and would like to remove, clean, and tighten all the main grounding points, as well as overhaul the battery box.

From what I have seen on the truck, and read here there are three main grounds?

-starter to frame rail
-alternator to frame
-front passenger side behind grill
-battery box ground
-clean all wires at the polarity box behind spare tire.

Is there anything else I’m missing?
 

Ronmar

Well-known member
693
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Location
Port angeles wa
There is no battery box ground, but like Suprman says it is probably a good idea to add one. While you are at it, it is probably a good idea to delete the shunt and run a cable direct from battery neg to starter neg. the shunt is only used by the STE and doesn't serve much purpose for us without the STE system. You can also easily delete the STE plug, freq divider and junction box up under the drivers dash(6 screws 3 plugs)...

The strap on the front right frame rail goes to the cab floor. On the other side of the floor it extends up to the ground lug in the PDP. Don’t forget that one...
 

Asymair95

Member
95
22
8
Location
Hudson Valley NY
So if I bring this thing to a cat dealer for maintenance they won’t need the ste/ice plug? Is that a DOD only interface?

Last night I found my issue I believe. The alternator mounting bolt that the grounding strap is bolted to was finger tight. Same one as Dave Anderson in his video.

I will still work on cleaning the grounds, and making sure everything is tight and sealed from weather. Trying to get the truck as reliable as possible.
 

Suprman

Well-known member
Supporting Vendor
6,711
111
63
Location
Stratford/Connecticut
The ice port is military only. The first gen trucks have a mechanical engine. There is a allison diagnostic connection but its separate. The a1 trucks have a computer motor and it has a standard diagnostic plug also. I can pull codes with a simple otc handheld reader.
 

Ohiobenz

Active member
Supporting Vendor
349
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28
Location
Seville, OH
There is no battery box ground, but like Suprman says it is probably a good idea to add one. While you are at it, it is probably a good idea to delete the shunt and run a cable direct from battery neg to starter neg. the shunt is only used by the STE and doesn't serve much purpose for us without the STE system. You can also easily delete the STE plug, freq divider and junction box up under the drivers dash(6 screws 3 plugs)...

The strap on the front right frame rail goes to the cab floor. On the other side of the floor it extends up to the ground lug in the PDP. Don’t forget that one...
Question about the shunt... the other side of it goes to the NATO plug negative terminal.
I'm in the process of rewiring for a 24v Bussman in the place of the PPD, pulling the 12v load off the 100A Bussman terminal.

So the NATO ground could just go to any solid frame ground connection, if I eliminate the shunt it doesn't need to run all the way back to the starter???
 

Suprman

Well-known member
Supporting Vendor
6,711
111
63
Location
Stratford/Connecticut
Adding a couple big grounds isnt a bad idea. You can leave the shunt setup. It isnt hurting anything. You can add the big frame ground. If you want to eliminate the shunt, remove it and just ground the cables there.
 

Ronmar

Well-known member
693
276
63
Location
Port angeles wa
Question about the shunt... the other side of it goes to the NATO plug negative terminal.
I'm in the process of rewiring for a 24v Bussman in the place of the PPD, pulling the 12v load off the 100A Bussman terminal.

So the NATO ground could just go to any solid frame ground connection, if I eliminate the shunt it doesn't need to run all the way back to the starter???
One side of the shunt goes to the starter neg terminal. The other side of the shunt goes to the batter bank negative terminals. The nato plug ground And plus leads should be connected at the battery negative And +24 terminals respectively. mine nato plug was was when I removed it, both leads were only about 30” long...
 
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