Joined: May 09, 2014 Posts: 83 Location: High desert Ca
Posted: Wed Aug 27, 2014 3:31 pm Post subject: Gauge me?
M38A1
Serial #6300 maybe #63000 I have a conflict with a Willys Overland new replacement plate and the brass plate on the dash. (It's hard to read) it looks like 6300 to me.
Engine #MD62534 with 040 stamped in just above the engine numbers.
This engine "did not" come with this jeep, it came with an L and a T84 in it.
So I'm chasing gauges now. The fuel and temp gauge. First off this jeep came with a selection of gauges. Four temp, four fuel and a couple oil pressure both mechanical and electronic. What's in the jeep, is it correct? I haven't got a clue.
Just so we get it straight, I have a stock harness with the (I don't know what they're called) bell like connectors on the ends, and who'd a thunk, some are missing.
I've ran continuity test on the wiring, OK, resistance test on the sending units, there's a measurement of resistance, maybe OK. I'm suspecting I have a mixture of 12volt and 24volt things going on plus the installed gauges aren't the correct ones from the get go. I have a temp gauge that has a 1ohm L shaped resistor on the back and marked 24volt. I wired this one in and it didn't work either. Some of these gauges have part numbers on them and some don't.
All of the gauges all have small differences. How do you tell by existing criteria what belongs in this thing?
How do you tell what side of the gauge gets the sending unit wire and which gets the #27 power wire. The things aren't marked as far as I can see.
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Wed Aug 27, 2014 6:05 pm Post subject:
Hammer,
I guess for our information it would help to know if the jeep is 12 volts or 24. Does it have two batteries? Does it have a generator versus an alternator. Is there a voltage regulator next to the battery in the engine compartment? 'Course you could always meter it. The more info there is will matter how everyone here can help.
First you need to go to the Photo Gallery and Wes' pages. He has a ton of stuff on the M38A1.
Next download TM9-8014 M38A1 Operators Manual, TM9-8015-1 Engine & Clutch Manual, and TM9-8015-2 Body & Powertrain Manual. One of them may have the gauges called out, but I think it may be just the whole gauge assembly.
The M38A1 wiring diagrams are on Wes' pages, but I don't see a gauge photo. Just not familiar with the M38A1 stuff.
ORD9-SNL G-740 is the list of all service parts for the M38. There has to be a comparable list for the M38A1.
I can tell you that the temp gauge you have with the L-shaped black connector is probably an original 6 volt gauge with a resistor for use with a 24 volt system. interesting that it is 10 ohms. They came with 95 ohm resistors for 24 volt. Use the search function above (not the one on the left) and you'll see some recent posts regarding not only gauges but the connectors. The metal connectors are called Douglas, and the black rubber ones are called Packard. From what I have read both were used at some point on the M38A1. There are several suppliers that carry parts and complete connectors.
All of the gauges have one or two sets of numbers on them if original or replacement military. One is just under the pointer and one is at the bottom of the dial if there. Those numbers will tell you a lot.
Joined: May 09, 2014 Posts: 83 Location: High desert Ca
Posted: Wed Aug 27, 2014 8:40 pm Post subject:
Let's see what I forgot this time.
Leave it up to me to leave something out. Two batteries? Check. Generator? Check. Monster regulator on lower right side? Check. 25.6volts on the multimeter?
Check? I think we could call it a 24volt system. Check?
I was digging around in a TM9 8014 and walla a diagram/picture of how to wire the gauge clusters. That was easy!
The temp sending unit I have is pictured in the 8014 on page 230 figure 120. Is it 12 or 24 volt?
How do you tell?
The temp gauge in the jeep is numbered #7389567. I have another one of these.
Another....7389567
Another....7728855 this is the one that has the L shaped resistor. I don't think I said it was a 10 ohm but a 1 ohm. It actually checked out to a .95 ohm.
3 fuel.... 7728852
2 Oil.... 7728853
So now that I have these numbers is there a cross reference?
I'm starting to think that the temp sending unit is the problem. I don't remember what motor it came out of or where it came from. For instance. If its for a 12voltsystem and I have a 24volt gauge or visavirsa.
I didn't read anything in the 8014 about what was 12 or 24 volt.
I am suspecting that the grounding on the gas tank might be a problem with the fuel gauge, everything is either painted or coated with bedliner. NOT very ground conducive.
I just read troubleshooting for cluster gauges on the downloads page. I'm sure it's the temp sending unit, it was reading zero ohms, cold. But the question still remains, what's the part number for this?
I just checked out Willys jeep parts in Yuma and they had five sending units. 6volts 12volts and one at 24volts part #7728855 / 804873. This is the only one that indicated it was 24volts.
Is there a part number reference on the downloads pages?
Thanks, just playen in the desert.
This is where you open up the ORD 9 SNL G-758 which is the parts catalog for the M38A1 and compare your numbers on your gauges to those in the catalog. If you haven't bought one then download it free right here at:
http://www.willysmjeeps.com/v2/modules.php?name=Downloads&d_op=viewdownload&cid=60
along with whatever other manuals you are missing.
M38's and M38A1's were 24 volt and the gauges used on all except the very early M38's were 24 volt as were the senders. The very early M38's had water temp, gas and oil pressure all older 6 volt gauges that used a 95 Ohm resistor (not .95). You can research the parts numbers for the earlier gauges by downloading our free copy of the ORD 9 SNL-G-740 for the M38 jeep parts catalog right here as well:
http://www.willysmjeeps.com/v2/modules.php?name=Downloads&d_op=getit&lid=95
And while you are into boning up on your jeep be sure to utilize the helpful manuals free for your downloading enjoyment and enlightenment at thes popular Mjeeps locations:
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Wed Aug 27, 2014 10:49 pm Post subject:
Hey Wes,
On page 151 of the M38 ORD SNL G-740 manual I've found something interesting.
Under the temperature gauge listing there are two, with separate ordnance numbers, and there is a notation that the second one is for vehicles after s/n 17855.
There are only one fuel and oil pressure gauge listed, but there are two sepoarate gauges with WO and AC part numbers, but only one ordnance number for either gauge, and the reference to the vehicle s/n is missing. The WO numbers of the first fuel and oil gauges are in sequence with the early water temp gauge.
Ammeter:
24 volt AC#1501244, WO# 118102, ORD# 7728854 All M38 production
The MC17855 was the cutoff for the ext vs int resistor gauges. This was April 1951. The ORD 9 referenced was dated September 1955. At that point the Army was not stocking the external resistor set-up so that single ORD# would automatically substitute an internal resistor unit when stock of the external resistor unit ran out and the installer just tossed the resistor.
Note this 6 vs 24 volt issue did not apply to the ammeter.
The November 1951 ORD 9 SNL G-740 only lists these #'s:
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Thu Aug 28, 2014 8:10 am Post subject:
Hi Wes,
Yes, I was referring to that gauge info in the 1955 G-740 that you posted.
Note none of the gauges in the 1955 publication say 6 volt.
Interesting also that Hammer apparently has external resistor gauges in
hand.
Next question is what is in his gauge panel?
While we are on the subject, I do not see any reference to a ground wire from the gauge panel to the dash. Is the assumption that sufficient contact is being made between the dash and the back side of the gauge panel with just the friction of the four twist lock screws providing the pressure?
Joined: May 09, 2014 Posts: 83 Location: High desert Ca
Posted: Thu Aug 28, 2014 9:22 am Post subject:
Hi Brian, when I bought this jeep it came with five toats full of extra parts. All of these gauges wherein one of them. The 7728855 gauge with resistor was just in with the mix. What's in the gauge panel is a 7389567, I believe the correct one.
I think there was more in parts than what I paid for the jeep.
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Thu Aug 28, 2014 1:16 pm Post subject:
AH.
Thank you Wes.
Quote:
"The cluster should be installed with it's four 1/4 turn fasteners. I never trusted these to provide an adequate ground. I always added a ground jumper between a bolt/nut on the cluster to one of the circuit breaker mount screws on the side of the cowl battery box. You can install a quick insulated spade or knife connector to this ground strap for ease of cluster removal.
_________________
Wes K "
At willys the paint was left off or removed where two metal parts needed to be bonded (grounded) to each other. Most restorers get carried away with Pretty and forget to not paint these areas or to remove the fresh paint after painting to insure good grounds are made. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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