Try running a jumper wire directly from battery voltage to the headlight connections and see if it brightens up. If not, try going straight to the frame or the negative battery terminal with the ground. I second the motion to check the dimmer switch, they're bad about developing high-resistance connections.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!