Unless you're using the signal from the dimmer switch just to energize relays, pulling the full current of both filaments through the headlight switch at the same time will probably cause the circuit breaker built into the switch to trip periodically.
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!