Been busy on the Polara over the last few months. Trouble is now that everything has been adressed, i have an electrical fault

Every time i switch on my headlights, the temp and fuel gauge go up until they are reading off the gauge.
The car has had a new voltage regulator, new headlight switch, all fuses checked and cables traced, checked and fuse box inspected all without fault. I know I need to rebuild the alternator as the voltage is fluctuating to much, but i dont know what else could be causing it.
I havent done anything to the electrical circuits in the car apart from adapting to halogen bulb headlights.
Any help would be great.
Cheers
Simon