Battery "disconnect" and a couple gage issues - '5

TonyMorreale · Post by **TonyMorreale** » Sat Jun 16, 2007 10:26 am

I won't be driving my M38 (24v, solid state regulator) for a couple weeks and want to disconnect the batteries or install a disconnect. From what I've searched on this site, all I need to do is disconnect the ground on the engine compartment battery and the circuit is dead thus slowing battery drain - correct?

A couple gauge issues - all new gauges, wiring, harnesses, regulator, batteries, rebuilt genny and starter, etc...

I don't think my temp gauge works (it's new with all new wiring, sending unit, etc) as it won't go up over 80 degrees. I know the engine is getting warmer than that when I run down the road. I'm going to try to test the gauge out of the vehicle, but could this be a working gauge and a bad thermostat?

Oil pressure gauge doesn't work either. Again, new gauge, wiring and sending unit. PO had a mechanical unit installed that seemed to work so I don't think the problem is in the engine passage to the sending unit, but somewhere from the sending unit to the gauge. Common problem?

Post by **wesk** » Sat Jun 16, 2007 11:25 am

Yes disconnect the ground cable on the underhood battery. If you buy a disconnect switch put it there also.

Use the M series gage troubleshooting service bulletin at:
http://www.cj3a.info/sibling/milgauge/milgage.htm
You can test the temp sender by removing it and suspending it in a pan of water. Then connect the hot wire and connect a jumper from the sender housing to the block. Put a good thermometer in the water and slowly heat the water and compare the thermometer to your gage readings in the dash with the switch on.

You can also pull the oil pressure and connect it the same way electrically and use an air hose and gage to apply pressure.

In either case make sure the sender is the correct part number sender to use with the part number gage you have. Especially the oil presure which came with a 0-60 PSI gage and sender and a different 0 to 100 PSI gage and matching sender.

TonyMorreale · Post by **TonyMorreale** » Sat Jun 16, 2007 12:30 pm

thanks Wes - will try /check these things.

cknight · Post by **cknight** » Mon Jun 18, 2007 6:34 am

Wes, you wrote the correct Oil gauage was 0-60. My gauage is 0-60. TM 9-8012 shows on page 221, 0-120. My book is a 01/56 issue. What would be correct?

Post by **wesk** » Mon Jun 18, 2007 4:56 pm

Actually I didn't say either was correct. I only mentioned that both exist. The 0-120 is correct for the M38. The 0-60 was retrofitted in the field to most M38's. Until sometime late 51 or early 52 the M38 used an oil pressure gage 0-120 with a resistor hanging on the back G742 7728853 then thru the rest of production the same gage without a resistor hanging on the back with sender 7728856. The M38A1 introduced the 60 PSI gage 7954230 and sender 7954231 between 1955 and 1959 and this was retrofitted to most M38's after that.

Jeeps4Brains · Post by **Jeeps4Brains** » Tue Jun 19, 2007 7:09 pm

So Wes, are you saying that theM38A1s before 1955 came with the 0-120 oil pressure gauge?

My 53 came to me with a non military gauge where the oil pressure line screws into a fitting on the back of the gauge. (I plan on testing this one and then using it when I test run the rebuilt engine.)

I have been looking for a 0-60 gauge but if what you say is right I need to start looking for the 0-120.

But then again I could just say it was a retro fit.