I replaced my factory bmw 740il radio with a kenwood but now have no sound. I only replaced the head

still have the original bmw cd changer in the trunk.

I replaced my factory bmw 740il radio with a kenwood but now have no sound. I only replaced the head unit and?photoshop

The factory amp only uses the + side of the decks output for speakers. You hook up the - and + sides and blamo the amp is dust. What I do when the amp is dust is go to the drivers side of the trunk and just uner the hinge area it a centeral point for all the wires. I identify all the wires with a wiring diagram and add capasitors (never spell that right) to the right wires to get the highs,mids and lows going to the right speakers. (a stereo shop usually has the "caps" under the counter in a pick a part box) I use a high power deck and it usually sounds better than the factory amp ever did.

Bunch of work and you end up with a 10lb wire blob in the trunk. The factory amps die all the time even without a new deck installed wrong.

Oh and I use the front speaker wires as the 2 additional wires needed to go to the back. Then I add new wires to the two pront speakers I choose as the wire donors...

I replaced my factory bmw 740il radio with a kenwood but now have no sound. I only replaced the head unit and?symatec

Your car is best left to an expert at an independent shop. I'm willing to bet your car has a factory amp. Connecting a new head unit to it is not for an amateur. Some amped systems are just very confusing and intricate. Personally, I'd stick with the stock head unit unless you have some strong reason to swap it. I hope you have a high-end kenwood too. Crutchfield.com probably can tell you if the car is amped, and they might sell an interface you can use. Oh, and hooking up your radio wrong can blow your factory amp, so be careful. Actually, that's how I got into car audio. Some doof blew the factory amp in my brand new car. Best of luck.