You could add an additional piece of wire to the wire you removed from the sending unit to make it long enough to reach with your meter leads.
But before you go to a lot of trouble, what happened when you did the steps a,b & c of "testing the sending unit installed in the tank (key on)"?
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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