I ordered a Kenwood KAC-8404 amp to add to my stock 09 Scab head unit. Right now I have a set of Boston S85s in the front door which I'm pretty happy with except that they start to break up before I'd like. Two channels will power those. After I get the amp installed and listen I'll decide whether to go to the next step and add a small sub, add a second set of S85's to the back doors, or move the S85s to the back and add a set of components to the front or some combination.

I'm definitely not going to run new speaker wire for the door speakers because I'm not willing to drill out the molex connectors, at least right now. My plan is to buy the appropriate Metra harnesses to make a T-harness to go between the radio and vehicle harness. I'll need to run several pairs of speaker wires back to the amp which is going to go under passenger side seat or maybe behind the seat back.

Since I'm going to have several feet of fairly small wire in the circuit, I'm wonder what gauge wire i should use for this harness?

 

you gotta run new wire if you power your speakers
your head unit puts out about 12 watts, that amp will do 50.
4 times as much power in the same size wire?
not a great idea

 

It would be safe. But it would make a tremendous difference to drill it.

As far as wire gauge is concerned you could use 4/0 if you wanted but 16-18 would be fine.