Thank-You for your replies, ended up getting it working.
Had to run all new speaker wire throughout the car which took a while but atleast i know it's done right.
The last guy's install was so sketchy though! Some of the RCAs were partly melted (talk about fire hazard). and he was using "Arc welding Cable" for the power (it's pure copper so i guess it works but like wtf?)
Nice and re-done and amp/subs are hooked up working perfectly. Thanks again for your help.