I need help as to how best track a short in my wiring of my guages.

I have a Track T roadster with a wiring kit, and am using Stewart Warner Wings guages.

The problem occurs when I have the headlights on and the gauges should be backlit. With the lights off, the electric guages work fine. On, the oil pressure and fuel level gauges peg.

I don't know how or where to begin to check for a short connection......HELP!

- Tom