I have a '49 Club Coupe on which I usually have to lightly tap the chrome frame on the gauge cluster just below the temp gauge to get it to come off C after the engine heats up. Then it records fine, but usually hangs up at C again every time I shut the engine off. I keep a half golf ball in the car to save my knuckles for this love tap, which everyone thinks is real funny. I have a 1952 Motor's Repair Manual that has a pretty good section on the AC electric type temp gauge. Maybe this will add some to the detailed response you already have. Check as follows: 1. Disconnect wire from binding post on engine unit and hold end of wire away from all metal. 2. Turn ignition switch on. 3. Check dash unit; the needle should point to the low mark C. 4. Touch the bare end of the wire to the engine block. 5. Check dash unit again; the needle should point to the high mark H. 6. If the dash unit does not indicate properly, first check the wire. If it is OK, replace the dash unit. If the dash unit is OK per steps 3 and 5, this indicates reasonable performance of the dash unit and connecting wire. In this event, they have you check the engine unit by removing it from the block and operating it in a pail of hot water with a thermometer for reference. Be careful not to immerse the portion of the unit above the block threads as it may ruin the unit. Also, you must ground the unit to the block of the car at some point below these threads. If it does not read OK, replace the engine unit.