Well...here's a slight development.

When I pull the plug from the back of either headlight, the other headlight gets almost twice as bright. Then, when I put it back, the radio goes out again, and the lights go back to being a little dimmer. Definitely looks like there is a ground wire screwy on one of the headlights.

Does this give anyone else any ideas? Or am I right to suspect a ground wire from one of the headlights?

1998 Isuzu Rodeo LS
3.2L V6