It's not necessary to disconnect any wires unless you just want to simplify things somewhat. Connect a heavy wire (#12 or #10) to the battery terminal at the starter switch, one long enough to reach the headlight terminal blocks. Touch the wire to each connector for high and low beam (stay away from the ground with the hot wire!) If the lights brighten up noticeably, I'd suggest installing relays that take the power directly from a battery source like that starter terminal, and use the wiring from the dimmer switch to power the relays. You'll need two 6 volt 30 amp relays, one for high beam and another for low, but they're very inexpensive, and Ebay has hundreds of them. Mount the relays on the radiator support close to the headlight terminal strips.
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!