Last night when I turned on the headlights, I noticed that both the temp gauge and Fuel gauge in my 120Y rose up. I turned off the lights and they returned to normal.

For those Electronics experts out there, am I on the right track by assuming there is a short in the lighting harness or is it something else...

I'll take all the advice I can get guys. Thanks...

I'm by no means an electrical expert, but I'll have a go.
I wouldn't be too worried about a short in the harness, i think it would more likley be voltage drop in the whole system as the lights are turned on. Gauges are funny things, and depending on how they work in relation to their sensors, different voltages may effect their readings. I've owned two early commodores, and the blinkers on both cars made the gauges tick in time to the flasher (even worse if the lights were on). Disconnect the lights at the globes, turn the switch on and if it still happens, then it may be a short (I think!!) But, like I said, I'm no expert on things that spark.

More likely a dirty/corroded earth strap, or a corroded connector from the dash loom to the enginebay loom.

Have you had the engine out lately? Check the earth strap from the battery to the body too.

Chris

the voltage regulator in the temp gauge has gone bad.
replace the temp gauge

If that were that then why is the fuel gauge also 'going north' ? Given that it only happened after the Head replacement, I'm inclined to think it is a bad earth. But as someone said earlier, gauges are funny things so Many Thanks for the input !!!