The C-3826 may be old but it was used for decades as long as the thermal gauges were in use. Based on my 78-81 truck parts book from Mymopar, as late as '78 the IVR was PN 3592899 which superseded PN 2258413 which is the IVR for the thermal gauges that C-3826 was used to test since the early '60's. Bottom line, I think the C-3826 tool is still the tool to use on your '74 and the 244 ohm sender you have is not the stock sender for a '74 Mopar. The values from the '93 FSM are not applicable as Mopar had stopped using thermal gauges by then. He said he is running the 93 cluster and wiring. Magnums had two temperature sensors one for the gauge and one for the computer. All correct, which is why I thought the 89 sender (196 ohm unit) would work as it looks just like the early units and clears my fuel line, but I guess I was wrong.  Not the first time and certainly won't be the last.
"Follow me the wise man said, but he walked behind"
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost conversion.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
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