Trouble shooting a possible short

1959 - 1978, M151, M151A1, M151A2, Technical questions and discussions, regarding anything related to the M151.
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bobtanker
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Trouble shooting a possible short

Post by bobtanker » Thu Jun 16, 2022 7:40 am

Guys,
Here is the background:
M151 with a replacement A2 harness. Everything working fine until a week ago.
Turned on ignition switch and the fuel pump energized. It is an aftermarket pump wired into #12 for power. All gauges dropped to 0 and starter will not crank.

Replaced the ignition switch, replaced the starter switch. Currently 24+ volts measured at the batteries with the ignition switch off, then drops to 3-7 volts with the switch on.
Batteries are fully charged

Disconnected the wire to the pump: no change
Disconnected the horn wire: no change
Disconnected the fuel gauge wire at the tank: no change
Disconnected the vehicle light switch: no change

When the ignition switch is turned the voltage meter initially goes to high yellow then quickly drops to 0. Sometimes the gauge "wobbles" as if a blinker is on. Vehicle has no turn signals installed.

Right now, I am at a loss on how to move forward. Any suggestions appreciated.
Thanks
Bob
63 Willys M151- "Tink"


svramselaar
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Re: Trouble shooting a possible short

Post by svramselaar » Thu Jun 16, 2022 11:09 am

Hi

I think you have a bad batterij or two sheck this with a controle light
If it lights up try to start is it go out bad battery
The other thing posseble is a bad wire connection from the batterij to the starter switsch
Do the same as at the battery's

Let us know the solution
1976 ? M 151 A2 AMG MUTT lost in acsedent
1978 M 416 A1 ( parkhurst ) trailer
1970 m151 A2 FORD BUDD tub
1957 Volvo sugga radio truck
M 274 mule HOME MADE MULE

markrdje
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Re: Trouble shooting a possible short

Post by markrdje » Thu Jun 16, 2022 11:33 am

I'd check water level each batt cell, also use a hydrometer to check charged liquid in each cell, though I'd think the voltage level would change while starting it, to add to what svramselaar said.
change user name to mark

Rickf
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Re: Trouble shooting a possible short

Post by Rickf » Thu Jun 16, 2022 1:40 pm

You do not need to turn on the ignition switch to be able to turn on the headlights. Have someone in front looking at then and switch them on. I am guessing you will get nothing or maybe and orange flicker. It sounds like bad batteries to me also but I have also seen corroded battery connection do exactly the same thing. Put a volt meter across he terminals of one battery and try a load and see what happens and then do the same for the other battery If you get a severe drop directly on the terminals then the batteries are dead. I should say bad, if they are holding a 12 volt surface charge and immediately dropping to 1.5 to 3.5 volts they are bad, beyond bad!
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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bobtanker
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Re: Trouble shooting a possible short

Post by bobtanker » Thu Jun 16, 2022 4:36 pm

Wow, am I embarrassed. I have completely failed in my PMCS. I apologize to every NCO I ever served with.

It was a battery. Low fluid in ALL cells. I fell victim to trusting technology, I had each battery on a trickle charger and failed to check the fluid level as I should have. It started right up every time and I became complacent. That came back to bit me in my fourth point of contact.

I will report to the 1st Sergeant in the morning for extra duty.

Thanks for the prompt responses and help.

Bob
Bob
63 Willys M151- "Tink"

Rickf
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Re: Trouble shooting a possible short

Post by Rickf » Thu Jun 16, 2022 5:34 pm

And Mark gets your next week off! I am so used to maintenance free batteries I don't even think of checking electrolyte levels anymore. I flat out refues to use overpriced and underpowered 2HN batteries.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

Fil Bonica
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Re: Trouble shooting a possible short

Post by Fil Bonica » Fri Jun 17, 2022 5:31 am

If you replace the batteries 51R is a good choice.
Much better performance.
Also keep in mind the jumper between the two batteries.
If its loose you have the same condition.

Fil Bonica


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