Jegs sells a plastic covered wiring schematic with colors same as original. Your gauges on your truck should be same as ‘47-‘55.
Ed in CO That supposedly 55 GMC wiring diagram shows a negative ground 12v battery and an overdrive, neither of which were available on 1st series 55 or earlier GMCs. I wouldn't depend on it.
'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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