So my truck has the SR5 package, and my question really pertains to the factory subwoofer behind the passenger seat.. My truck when I bought it had an aftermarket stereo already and the previous owner also replaced the door speakers.. But my problem is that the sub is not working? I have too much highs & mids but no bass... Any one know if you have to have the factory amp hooked up or did whomever installed the replacement radio just not hook it up... So I guess my real question is can the factory be used with an after market head unit? Thanks in advance..

The external amp that drove the speakers would be disconnected if you put in any aftermarket head unit. You could tap into the factory amp if you used a Y-adapter fer the power/preamp wires. Not sure on the pinout but it could be done.

If you remove the center cover near the transmission hump, you should see if it's still in there or if the previous owner removed it. If it's gone, then yer probably better off hooking up yer own amp or gitting one from a parts yard. <img src="/forums/images/graemlins/smile.gif" alt="" />

Is the factory amp 'speaker level' or 'line level' input?

If it is speaker level any headunit can drive it.

Maybe the rear speaker could simply be connected to the headunit's output for rear speakers?