Electric Problem on a Ford 2000 tractor?

I've replaced the front and back wire harnesses, ignition switch, light switch, voltage regulator, and intrument cluster on a Ford 2000 tractor (3 cylinder, 1970). The panel lights stay on even when the key is off. I've quadruple checked the ignition wires and have tried removing wires one at a time from the instrument cluster. I've removed all the wires from the light switch and the instrument panel lights remain on. Anyone have any suggestions?