willysmjeeps.com

It will be interesting to see this new service bulletin. I haven't found one yet.

On another note I will point out again the M170 sender and gauge are different and not meant to be used on the M38 or the M38A1 and the M170 has a different shape and volume tank that holds 20 gallons when full vs 17 in the M38A1 and 13 in the M38. So mix and matching does not work well between these three different fuel systems.

Ohm readings for sender 1200923-2
1.8 ohms empty (float down)
24.4 ohms 1/2 full
40.5 ohms full (float up)

Ohm readings for sender 11640674
3.4 ohms empty (float down)
16.1 ohms 1/2 full
32.9 ohms full (float up)

Both floats go up and to the right (with Douglas connector facing forward). The original sender float went up and to the left.

1952 M38
Fuel gauges tested: 7728852 AC 1517561
Gauge reads empty with float down. Gauge reads full with ground removed. Gauge reads slightly over 1/2 full with both senders float up.

Your results only point to two possible culprits. Mismatch caused by senders resistance or gauge malfunction. I would suggest your next step is getting the correct sender since it is obvious they are not the correct part number.

TB ORD 659 does not mention the resistance value of the sending unit. I like the last paragraph "Note".