Post Master General
Join Date: Apr 2012
Location: Bowling Green, VA
I Ride: '09 ZX6R
If you don't want to damage the wiring harness, you can simply tuck a fine wire into the fuse holder for the headlamp circuit..... that will give you a power condition only when the headlights come on.
Use that light wire to provide the juice to a relay coil, so that relay only completes its circuit when the headlight comes on. The common pin of the relay should be fused, and go to the positive battery terminal. If you are using this 12V port to support USB devices, the fuse should be quite small in Amperage. I would recommend the smallest you can find -- probably 1 A, which is far more power than any USB device can accept.
Wire the positive lead of your outlet into the normally open side of the relay, and leave the normally closed side without anything attached. Negative side should be tied back to the battery; but that can be done anywhere that the harness is connected to the negative pole of the battery.
"There's this adage that we have 2 ears and one mouth so we should listen twice as much as we talk. Unfortunately with the Internet people have taken this old adage and turned it around. They have two eyes and 10 fingers so they think they need to post 5 times as much as they read. And since they have 10 fingers and one brain, they only have to think 10% of the time! "