M151a1-a2 wire harness difference?

1959 - 1978, M151, M151A1, M151A2, Technical questions and discussions, regarding anything related to the M151.
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matt506
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M151a1-a2 wire harness difference?

Post by matt506 » Sun Oct 29, 2017 4:47 pm

Ok picked it up and on my way picking up parts for the future. I know that the A1 wire harnesses are rare as hens teeth. So what are the tricks every one has been doing to rebuild their existing harness? Are A2 harnesses pretty different or is this a added wire and some connections swapped out?
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Re: M151a1-a2 wire harness difference?

Post by markrdje » Sun Oct 29, 2017 6:07 pm

The 151a1 has no electric wipers, has electric fuel pump, that's all I can think of at the moment
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Re: M151a1-a2 wire harness difference?

Post by Rickf » Sun Oct 29, 2017 6:20 pm

The A1 has the #77 circuit which includes the oil pressure safety switch and the fuel pump circuit and an extra circuit breaker. It is not a big deal to add this to an A2 harness. Or you can convert to an A2 fuel pump on the egine and run an A2 windshield with electric wipers. Another option is to use the electric wiper circuit to power the fuel pump. There are several ways to get around that one. Another issue is the 25 amp charging system that would involve a bit of changes to the wiring unless you went to a 60 amp alternator in which case it is a bolt on and plug in. You would need the three belt pulleys. The only other changes are that the wires at the turn signals need to be extended a bit since on an A2 everything is together in the composite light.
1964 M151A1
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Re: M151a1-a2 wire harness difference?

Post by Gary Turman » Sun Oct 29, 2017 9:26 pm

I used an nos A2 harness in my A1. Worked well but as mentioned no oil pressure cut off and I used the wiper power for my fuel pump but had to use a extension about 6" long.
1941 Dodge WC-7 Command Car
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Re: M151a1-a2 wire harness difference?

Post by matt506 » Mon Nov 06, 2017 3:52 am

Tons of help thanks guys. I think with the info from you all I am going to go two of ways depending how the original front harness is.
1. With a new rear harness on the way i will use the old one and repair the existing front one. Or
2 .If the front one is to brittle, use both the old front and rear harnesses as donors to retro fit a new A2 harness to the older 151 needs.
SFC Matt Miller,
4-42 GPW,
M-6 81mm hand cart,
4-43 MBT,
4-43 WLA,
1961 M151,
M18 paracaisson,
"Find The Bastards and Pile On" 11th ACR

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Re: M151a1-a2 wire harness difference?

Post by Fil Bonica » Mon Nov 06, 2017 5:53 am

If you are using a replacement A1 rear harness you might want to cntinue to use the low pressure oil switch.
Recently finshed an A1 harness replacement .
It took some extra work but the safetry switch function was saved.

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Re: M151a1-a2 wire harness difference?

Post by matt506 » Mon Nov 06, 2017 8:03 am

Yes that is why i would like to save my front harness as that part is still there. Biggest problem is a lot of front light wires have been cut and converted to conventional 12 vold head light stuff or just cut for front blackout lights .
SFC Matt Miller,
4-42 GPW,
M-6 81mm hand cart,
4-43 MBT,
4-43 WLA,
1961 M151,
M18 paracaisson,
"Find The Bastards and Pile On" 11th ACR

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Re: M151a1-a2 wire harness difference?

Post by Fil Bonica » Wed Nov 08, 2017 6:21 am

If saving the harness is impossible consider making up an add on sub harness for the oil pressure circuit.
It only requires three wires a circuit breaker and connection to ignition switch starter and pump.
If you need help let me know.

Fil Bonica

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Re: M151a1-a2 wire harness difference?

Post by acudanut » Sat Nov 11, 2017 7:06 am

markrdje wrote:
Sun Oct 29, 2017 6:07 pm
The 151a1 has no electric wipers, has electric fuel pump, that's all I can think of at the moment
[/quote
What year did the M-151 go to an Electric Fuel Pump. ??

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Re: M151a1-a2 wire harness difference?

Post by Rickf » Sat Nov 11, 2017 7:47 am

1959-1969. When it went to A2 it went to the mechanical pump.
1964 M151A1
1984 M1008
1967 M416
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12/1952 M100- Departed
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Re: M151a1-a2 wire harness difference?

Post by redcoat54th » Fri Jun 15, 2018 9:54 am

Question: how important is the A1 oil pressure cut off? If the A2 does not have it was it protected in another way? I am fitting the A2 harness into an A1 with a 25amp system. Thanks in advance, Bob
British Army (Royal Signals). US Army 1st Air Cav (UH1H pilot)
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Re: M151a1-a2 wire harness difference?

Post by Rickf » Fri Jun 15, 2018 1:26 pm

The A2 has a mechanical oil pump so no need for a oil pressure safety switch. When the engine shuts off so does the fuel pump.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Re: M151a1-a2 wire harness difference?

Post by redcoat54th » Fri Jun 15, 2018 1:28 pm

Thanks Rickf that clears it up. Cheers, Bob
British Army (Royal Signals). US Army 1st Air Cav (UH1H pilot)
Prime mover 1965 M151A1
Trailer M416
MVPA #37617

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Re: M151a1-a2 wire harness difference?

Post by muttguru » Fri Jun 15, 2018 2:28 pm

Hmm..the M151 and the M151A1 have an in-tank electrical fuel pump. The M151A2 has a mechanical fuel pump.

The main purpose of the low-oil-pressure safety switch is....if the M151 or A1 vehicle stops running (such as in an accident or rollover) the oil pressure drops (the engine stops running but the fuel stops pumping). If the fuel pump continued to operate, imagine the vehicle lying on its side with fuel pumping all over the place and you pinned in the driver's seat !

Additionally, if the oil pressure drops for other reasons (cracked sump, loose drain plug etc) the oil pressure will drop and the engine will shut off, preventing damage to the engine.

Problems with faulty oil-pressure safety switches persuaded the Mil to change over to the mechanical pump fitted to the A2-series.....it was a trade-off between safety and reliability.
Ken
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Re: M151a1-a2 wire harness difference?

Post by redcoat54th » Fri Jun 15, 2018 3:03 pm

Thanks Ken, than makes sense. I have converted from the electric petrol pump. Now I would like to convert to a 60 amp alt to make the A2 wire loom a little easier but money says I might consider running the extra wires to the 25amp genny. Hope all is well with you in the UK., Bob
British Army (Royal Signals). US Army 1st Air Cav (UH1H pilot)
Prime mover 1965 M151A1
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