I need help with a car audio wiring problem, must know what your talking about?

[Juston]

Im trying to hook up my adjustable line converter to my rear speakers to hook up my amp to my stock radio and i accidently bought 16 gauge instead of 18 i really dont want to go back to the store i was an electrician for a while and i know when you ran a lower gauge (like an 8) to a higher gauge (like a 16) it only transmitted the current the 16 could carry. its gonna be runnin the 18 from the car to about a 2 foot strip of 16 back to 18 on the converter, im almost positive it will work i just dont want to blow it and buy another one