OEM wiring is old and if never cut up it can be used but new is always better. I am cheap and never hd an electrical fire . Maybem lucky, maybe just good>> I have always used the oem under dash harness if not cut up. Yea and I use the oem amp gauge too. If the dash harness if out of the car on a bench, an untrained monkey an ou it all back with a FSM. :BangHead: