Yoshimura fender eliminator light issue?

Was splicing together the wires today for the license plate light on the Yoshimura fender eliminator and the solder in the center of this shrink didn’t want to melt like the other one did though I heated it up a lot (maybe just bad solder?) I wrapped the two wires together and then put electrical tape over the shrink sleeve. Do y’all think that will be good enough or do you think it’ll rattle loose?