Squirt the end of the conduit full of clear RTV just before you slip it all the way onto the rubber grommet at the back of the light, then tie a knot in the wires at the other end to hold the conduit tight against the back of the tail light. When the RTV hardens, you'll have a semi-permanent installation of the conduit over the wires. If you ever need to remove it, use a heat gun on the outside of the conduit to soften the RTV.
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!