I bought my trans am with 2 aftermarket autometer guages on the left pillar. (water temp and oil pressure). Before i did the t56 swap they both worked perfectly and they it up. Now i have finished everything, but ive noticed that they work until i turn my headlights on then the guages go all the way to the right, pretty much says im running at 260 degrees and like 100 psi oil pressure. I can turn the dash lights all the way on and they will work, but they go all wonky when i turn the headlights on.

Like i said i bought the car with them already wired up and ive never installed aftermarket guages before.. where should i start investigating?

 

definitely could be a grounding issue, so I would double check your grounds from the gauges and from your headlights since that seems to be the main culprit, also check to make sure you power wires from your gauges are not contacting the headlight wiring