M38A1 Ammeter to Voltmeter (Y,R,G) Conversion -"SEND&qu

colmustard · Post by **colmustard** » Sat Oct 31, 2015 8:50 am

I have a 53' M38A1 and I want to replace the ammeter with a voltmeter that I came across because the ammeter isn't working.(Proper Voltage exists on wires 8 & 9, but my gauge reads open circuit) Voltmeter is a newer military vehicle style with yellow red and green indicators. According to the gauge troubleshooting manual link that was posted on some other topics, when this voltmeter is hooked up to my ignition switch outlet I should have yellow battery power (wire 27) and when I start the jeep I should get regulator output power which would push it up into the green area on the gauge. My problem is I don't know what wire to use to get regulator voltage output. Should I try 8 or 9 to SEND? ( I'm afraid that will fry my gauge)
The gauge has three connections IGN, GND, and SEND. So what is the proper connections to IGN and GND and SEND to get full functionality of the gauge? [/img]

4x4M38 · Post by **4x4M38** » Sat Oct 31, 2015 9:52 am

If you still have a generator you should be able to use the ammeter.
Have you tried the troubleshooting process? An open sounds like
a bad ground, or maybe a shunt gone bad.

If you are sold on the voltmeter anything downstream of wire
#10 should be regulator output. Wire 27 should be the same.

Ign suggests to me you hook up wire 27 there to get voltage
only when the ignition switch is on. If you have a five wire
spider you can use the extra wire to hook up your voltmeter.

Send I am not so sure.

I have a military voltmeter and it only has two connections

Take care,

Post by **wesk** » Sat Oct 31, 2015 5:09 pm

Bottom line here is the voltmeter in question is not the correct volt meter for any M38/M38A1/M170 that has been converted to a transistorized voltage regulator. They used a single wire meter. Weather it reads yellow, red or green when the master switch is turned on depends on the battery's state of charge. It won't always be yellow.

Best advice is get the correct meter.

http://willysmjeeps.com/v2/modules.php? ... highlight=

http://saturnsurplus.com/gauges/9512.htm

4x4M38 · Post by **4x4M38** » Sat Oct 31, 2015 6:19 pm

Hi Wes,
One can use a voltmeter with a system without the alternator
right? Just have to tap into the spider for voltage.

Post by **wesk** » Sat Oct 31, 2015 8:19 pm

If you have read any of my previous posts and how to's on this topic you would already know the answer to that question.

Of course you can. What made you think you can't.

Don't misread my post above. I only pointed out that when the US military converted any of it's M38/M38A1/M170's to transistorized voltage regulators they always used a single wire volt meter not a 3 wire volt meter.

colmustard · Post by **colmustard** » Sun Nov 01, 2015 12:05 am

Well, thanks but buying a $65 gauge is not an option at the current time, (kind of like the NYMETS winning the series- not going to happen!) The gauge I'm quite sure is from either a M939 series 5 ton truck or an M1070 HET. since it sounds like no one really knows what the SEND wire should be, I will resolve to hook up either wire number eight or nine because reading the troubleshooting manual there should be a change in voltage and the colors are clearly mentioned therein; with The ignition turned on, yellow, green after that when the alternator kicks on.i will hook it up and let you know the results.

4x4M38 · Post by **4x4M38** » Sun Nov 01, 2015 7:07 am

Which regulator do you have?

Before wring your voltmeter to 8 or 9 read the post below:
http://www.willysmjeeps.com/v2/modules. ... =voltmeter

Post by **wesk** » Sun Nov 01, 2015 8:28 am

Why not just refer to the proper wiring diagram for the truck the gauge came from?

You mentioned you have an alternator in your last post. I find it odd you would use an old M38 mechanical voltage regulator with any modern alternator.

colmustard · Post by **colmustard** » Sun Nov 01, 2015 8:59 pm

Let me settle a couple questions that are still out there--

Brian, my voltage regulator is a A replacement Delco Remy mechanical regulator it is not transistorized.
I have 3 ammeters in my hand that came with the jeep, kind of like extra parts. They are the original gauge, one that shows 60+ and 60 - , another that shows 30+ and 30- and none of them flinch or move with wires number 8 & 9 connected. And I checked eight and nine and they had 28 volts on both which is correct. I have not looked into the shunt but I will look at that before too long.

Wesk, I miss spoke when I said alternator, I have a mechanical voltage regulator and a generator. Also thanks for the tip, I will go look up one of those manuals for a 5-ton and see if I can find that gauge in there.