lilbear - I have a Liftmaster opener. Any suggestions/help is appreciated.
Lifmaster remotes typically use a 3V lithium battery which adds a little to the circuit, but still not difficult. I also believe that the onboard Liftmaster receiver is compatible with Genie "Code Hopper" remotes which operate on a single 12V battery (the tiny newer models use a 3V coin though). With the proper remote programmed or "married" to your opener, you can easily install it on the bike. If it is simply a 12V battery operated remote, remove the battery from the remote, solder leads to the battery terminals and also solder in a jumper across the remote button contacts on the remote. Attach the leads to ground and your high beam leads on the bike and every time you flip on the high beam, the garage door opener will transmit. You can further complicate the circuit by adding pulse fire relays and transmit timing capacitors, but it is overkill and not at all necessary. If your remote operates on a voltage other than 12V, you will need to add a divider network to drop the bike voltage to the proper operating voltage of the remote. (PM me with specifics and I'll let you know what you need). Of course, it is easiest if you can find a compatible remote which operates on 12VDC.