I replaced the gauge, sending unit, and IVR.
You still could have a bad component in there. Ans since you had a short you could have damaged a wire which can cause all kinds of intermittent issues.
Ford gauge circuits were not not rocket science. The gauges operate on ~5VDC produced by the stock IVR 'pulsing' between 0 and battery voltage. The oil, temp, and fuel senders basically are all are variable resistors that go from 10 ohms (High OP/Temp/Fuel) to 73 ohms (Low OP/Temp/Fuel). The guages are fed 5V from the IVR on one side and are connected to their variable resistance senders on the other. The gauges are not -and should not be- grounded but the IVR must be well grounded to operate. If the IVR is bad then ALL gauges will have problems. If only one gauge is having issues (or, conversely, only one gauge is operating normally) the problem is NOT the IVR.
Okay. Engine Stop. ACA out of Detent. Mode Control, both Auto. Descent Engine Command Override, Off. Engine Arm, Off. 413 is in.
-Buzz Aldrin, Apollo 11 LMP
Actual first words from the surface of the moon
Early Fox: 5.0L HO SEFI conversion, 5-speed, 8.8 w/3.27:1 TL, full dual exhaust
1968 coupe - Ordered 12.15.67 Delivered 2.1.68: 8T01T, 65C, 289 conversion, hanger queen