I'm not sure I want to mess with that headache of trying to get the wiring through the door jam etc

If I run the amp wires up to behind the headunit and splice into the wires going to the door components, will the stock wiring be able to handle it?

Wires from the amp are 12 gauge

Lemme know! I'm almost done with all the wiring!

 

How many "rms" watts is the amp?

Any unnecessary connections between amp and speakers is never a good thing, and kind of makes any good speaker wire pointless, [ also IMO 16ga wire is more then enough for high-pass speakers] 94

 

It's the Alpine MRV-F340

 

OIC, 35W rms into 4 ohms @ 12V, 55W @ 14.4V, and although with the extra connections and the much thinner oem speaker wiring there will be some loss, but as long as you do not drive the amp into "clipping" it will work, however if you like it loud, the thinner wire will have a hard time carrying the current and can overheat and burn, although I have seen this happen on more then one occasion, it only happens when amp is driven into clipping, so if you keep the amp from clipping then the only problem will be a loss of SQ. 94

 

If its over 75 watts per channel I would not do it. If under you can get away with it with min sq loss. Its really not that big of a loss unless you are pushing a real good speaker/ amp set up. I do it this way if the customer can't afford the extra labor to pay for it. Like fcm said hust make sure the amp does not clip and you will be fine. If you are doing it your self pull the wire thru the door its not hard.