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Thread: Correct Batteries for 1955 M38A1

  1. #1
    Junior Member
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    Correct Batteries for 1955 M38A1

    Hello all. New here. I have a 1955 M38 A1. I recently replaced both batteries with "AutoCraft Deep Cycle Marine/RV Pro 24DC-2" batteries. Since doing so, I have no electricity, nothing. No lights no cranking...nothing. Both batteries show a full charge. My question is: am I using the wrong batteries? Prior to replacing the batteries, I had power. I replaced them because they were damaged. I accidentally touched a positive to a positive and one of the terminals "welded" itself to a post. Is there a fuse or circuit breaker I may have blown?

  2. #2
    Senior Member
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    I would bet that is the case. If you have proper voltage in your batteries, I really don't think that is the problem. I'll bet there is a circuit breaker somewhere that is the problem. Especially on the military models, I'm sure there was more protection for the system than on my CJ-5, for instance. One of the experts on here can probably give you more specifics.

  3. #3
    Super Moderator gmwillys's Avatar
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    There are a couple of in line fuses up under the dash. I would first check to ensure that the positive to the starter has battery voltage, then check the ground going to the voltage regulator tray. If both check out good, I would then trace the power to the ignition switch to see if you have power there. If you have no power at all, then that would be the first order of troubleshooting. There are some schematics available on line, but would highly recommend purchasing/downloading the military TM manual to have a complete break down of the circuits.

  4. #4
    Super Moderator LarrBeard's Avatar
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    M38A1 No Power

    M38A1 – No Power

    No cranking, no power to lights and accessories. – Hmmm. – that’s a clue

    You need to go and Google TM9-8014 and then download a copy. That is the M38A1 bible – it tells all about your vehicle! (Wow - sorry about the shout)

    But - remember - over the years someone may have done some new and improving; either formally or at a Motor Pool somewhere. Never say "No one would have ____________."

    According to TM9-8014, Para 161: “A single circuit breaker in the generator regulator protects both ignition and lighting systems from overload.” Since that breaker is buried in the sealed box, it is a thermal breaker that should reset once the overload is removed. It won’t have any effect on cranking.

    There are no fuses or breakers in the cranking circuit. The starting circuit is a very simple circuit.

    Go to the TM, Page 186, and look at Figure 89. Battery B is the one on the outboard, passenger, side. Battery A is the one closest to the midline of the vehicle.

    Battery B’s negative terminal is connected to ground through Cable 7. Battery B’s positive terminal goes to Battery A’s negative terminal through the jumper, Cable 68. Battery A’s positive terminal goes to the starter via Cable 82.

    The cable on the starter actually connects to the foot switch on the starter, check Figure 87 in the TM.

    Check all of the connections up around the batteries. Make sure that Cable 7 is making a good ground where it ties to the chassis. From Battery A positive to chassis ground you should measure 24+ volts. If not, you have an open cable or connection. Follow down Cable 82 to the terminal on the starter. You should have the same 24+ volts there.

    The lighting and accessory circuits are fed from the connection at the starter. Since you get no crank and no accessory power, it looks like you’re not getting power down to the starter terminal. Check all the connections again.

    M38A1’s are notorious for having one battery discharge. The reason varies by vehicle, but accumulated crud, carbon dust and such in the foot operated switch on the starter are sometimes the culprit. A battery disconnect is really a good idea in an M38A1 just to help your sanity!

    Let us know what you find- and post a picture of the critter.
    Last edited by LarrBeard; 06-15-2020 at 09:34 AM.

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