I have had to extend the wire on a B&M headlight because they didn't expect a user to put the light where I did. If you are using a dyno powered tail light, then the cable has to be long enough. I have used wire ties and also Gorilla repair tape to hold the wires on the bike.
Otherwise it really depends on the mounts and where you are going to place them. If you have some idea of what bike, that would be helpful. For example, most dyno headlights are meant to mount to the fork crown, and they work best there, but they might not come with a bolt that works on your fork.