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So, about the middle of last month, my gas gauge just stopped working. The gauge wasn't responding to any current, so I figured it was the gauge, and got a new one from John at Midwest Military. Still nothing. I tested the sending wire, it was fine. I tested the spider harness. It was also fine. So I figured it must now be the sender. I ordered a new one of those from John. Still nothing. If I connect current to the sending side of the gas gauge, it drops below zero. Otherwise, nothing.

The gas gauge registers the amount of ground . Take your drivers seat out and pull the sender back out. Power goes in one side of the gauge and out to the sender. As you move the sender arm up and down it changes the amount of ground the gauge gets. You most likely need to run a ground wire to the sender itself ( one of it's mounting screws ). Attach the other end to a seat mount bolt. You have to read the wiring diagram to see which socket on the back of the gauge the power from the spider goes to. They are very finicky about a clean ground at the sender. John

Go to Downloads, M-38. 5 categories @ top and select Electrical.
Go to pg2, 4th item down for detailed info for testing ALL your
Gages and senders.

You can always just look in the tank, thats free

Gas tank is about half full Bretto. So, if I have nothing attached to the sending side of the gas gauge, it should read full? And if I have it grounded, it should read empty? That seems to be what the manual indicates

Dan,

If you use the military TB for troubleshooting your gauges it will take you directly to whatever problem you have. You need to slow down, read the guide all the way thru and follow the guide step by step.

A lot of what you are now posting does not make a lot of sense when compared to each step in the guide. If you are having trouble interpreting your test results then post the results here using the test step number and letter.

Here are the test step results items you should be able to give us to help you.

5a Tell us what your battery voltage was.

5d Tell us what the volt meter read.

5e Tell us what the volt meter read.

5k Tell us what the fuel gage read.

5L Tell us what the fuel gage read.

5q Tell us what the fuel gage read.

6c(3)(a), (b), & (c) Tell us the result you obtained for each of these three checks.

My voltmeter is broken, but my voltage gauge works, and says the battery is putting out a good voltage. I tested the side of the gauge that receives battery current, and the circuit tester lights up. All my other gauges work as well, and the vehicle starts with no problem. I'll buy a new voltmeter gauge, possibly today, but that would seem to indicate that 5A, 5D, and 5E are all fine.
For step 5K, where I ground the sending gauge side of the gas gauge, it stays at empty, where it is anyways. For step 5L, where I removed the ground from the sending side of the gauge, with the ignition on, it still reads empty.

I'll buy a new voltmeter gauge, possibly today, but that would seem to indicate that 5A, 5D, and 5E are all fine.

That's an incorrect assumption. 5E determines that the gauge to panel ground is a good one. You must do both D & E with a digital voltmeter and the readings must be the same or you have a bad gauge to panel ground. These tests are aimed at the instruments, the senders and the instrument cluster mounting. That dash volt meter is only giving battery voltage reading. Get a good digital voltmeter and then come back here with the readings.

Based on Gauge behavior and if we assume that the voltage readings you did not obtain for steps D & E are identical and good, this would indicate a good gauge to cluster panel ground then the new gauge would be bad. So before you call John at Midwest get a volt meter and complete the test properly.

I assume you meant your electrical test multimeter is broken?

Dan, you need a good multimeter, it does not need to be expensive.
A good one can be had for as little as 25 bucks and can save your arse
in many situations. As Wes pointed out you need to slow down a little,
go thru the test proceedures outlined in the downloads and accurately
post your results. I used these test proceedures and followed them to
the letter and within an hour i had isolated my 2 gage/sender problems at 100% accuracy before i dropped a dime on new parts. Sure beats throwin
money at new parts you may or may not need. The bonus here is that
you'll walk away with a complete understanding of how the 24V instrument
set-up is designed to work.

Rick, you're right. My voltmeter broke, and I was just being stubborn. I got a new one today, and here is what is reads:
5.a check
5.d 24.5
5.e 24.5
5.k gauge reads empty
5.l gauge still reads empty
5.q gauge reads empty
I tested, and the tank is grounded. I'm not quite sure how to do the rest.

Your 5q result is not a valid result. That test assumes the gage is hood.

Your tests 5d, 5e, 5k & 5L have already determined that your gage is bad.

Test 5q must be performed with a known good gage. Once you get a known good gage installed then continue with the tests 5q and on.