There is an easy way to sort out if it's ground or voltage with a Volt Meter.

You need to find a brown wire someplace like any of the lights in the center dash, or even the light bulb down in the shifter if you have an auto tranny. Hook your meter neg up to chassis and the meter red lead to the brown wire. With either the light switch in the middle position or headlights on with the ignition switch in II measure the voltage.

You get voltage and no light, then check the ground it has to be missing. You can prove that by connecting a wire to the where the black wire goes and touching the other end to chassis also.

However if you get no voltage and no light and its back to the dimmer switch and fuse panel.

Regards,

Paul