I converted my 73 cutlass supreme to a floor shift and installed a rally guage. When I start the car, guage works fine(1st pic), when I turn on headlights the gas and oil needles go all the way to the left and temp goes right(2nd pic) and when I put the car in drive, guage works ok(3rd pic) but only in drive. Anyone have any ideas what the problem could be?

 

Check for secure ground connections for the gauges, and for their backlight lamps.
Also check the ground straps from the engine block to the body (and from battery to chassis). Make sure they are there and secure.
Sounds like there is a ground differential somewhere.

The tach in my ford died when the lights were turned on - it was a bad ground from the tach.