Some of the dimmers have a 3-prong plug with blade terminals on the switch. Others just have three screw-terminal connectors. Find the wire that's hot when the headlight switch is turned on by using a test light or a voltmeter, then connect a jumper from that wire to each of the other wires one at a time. You should get high and low beam lights as you swap the jumper. If none of the wires at the dimmer are hot with the switch on, you need to backtrack to the headlight switch and check it out.
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!