by thomas » Tue Mar 24, 2015 4:55 pm
It's electrical, it's an easy retro-fit. All the wiring for it will be present, at the back of the instrument cluster through the multiplug to the printed circuit board (which PCB ages badly), to the other end in the engine bay it emerges with the small bunch of wires that connect to the coil live feed and the oil pressure switch, it may simply have been cut back and taped over on the cheese-paring models with no temp gauge, and unravelling the loom back from the coil, just a couple of inches should uncover it. This wire will need to be extended out to the temperature sensor on the front of the head, and maybe need some durable loose outer covering against heat as it crosses the head. I think with the larger HB type sender, the heater hose at the back of the head could have connected where the sender is and the sender at the other, rear end of the head, where the heater hose is attached. This original HB 1159cc sender/sensor unit is necessary, being a larger size than the later HC, Chevette, Cavalier thinner senders; the Viva GT type is unsuitable too, early HC's might have used the same sized larger sender unit but calibrated for the HC instruments. The different senders have different temperature/resistance characteristics, I've found with a Chevette temp sender, as my HB has a later engine with the thinner, later type sender tapping, a 47ohm resistor in the sender's line brings the HB gauge near to spot on in calibration, without the resistor it registers far higher than the actual temperature.
Worth fitting the original gauge; as well as the actual gauge head unit from another instrument panel, all you need is a sender unit to screw in and it'll just work.