As a reference 14AWG copper wire is used in your home for a 15 amp circuit. It can carry much more but gets warmer. Tail lights won't be any where near that,probably less than an 1 amp? If you have 6 volts or even 12 volts the smaller wire has higher resistance and you might not get the full voltage out to tail or head lights going smaller. I think the more important issue is ground. I am going to run a sepearte ground wire to a point close to the battery ground connection.
