Picture two with power on, signal wire not connected (0 ohms) it goes to full as it should. No, with the wire disconnected the load on the wire is infinity ohms, not zero ohms. But you are right that the gauge should read full (at 30 ohms or more).
'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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