most likely 18guage.
when adding an amp and door speakers i would always suggest upgrading to new wire of at least 16gauge if your gonna be running anything over 50watts. might not make a difference but overkill is better then choking the power from getting to your speakers.
hn155: Rockford punch pro speakers, t400.4 deh 80prs, full audio build to come. working towards 175hp n/a, simple but fun.