It is possible that 1) the radio is dead, 2) the wires have been cut, or 3) the speakers are dead.
First, you have radio playing to the rear speakers. So either half the radio is bad or just no signal to the front speakers. Try hooking a KNOWN GOOD speaker to test the connection at each of the front speakers. Disconnect the speaker wires from the door speakers, and make a temporary hookup to the KNOW GOOD speaker while the radio is on. It is important to make sure the radio is on (YES, we all do dumb things sometimes.) This will check to see if you do have power to the speakers.
If nothing, try to tap into the wires on the back of the radio (you need a schematic for this one) to get the + and - for one of the door speakers, and use this new wire to try the KNOWN GOOD speaker to work. If nothing, then the radio is the problem.
It is possible that the speaker wires were cut between the radio and the speakers, in which case you will need to rewire the front speakers.
Unless you really want the factory radio left in, I would replace it and put it up for safe keeping. I removed my factory radio to keep for later and bought a good radio from Crutchfield for everyday. It is nothing to remove the new radio, frame, and wiring adapter from the car, and return it to OEM. (Well, almost nothing. [img]

It does take a while to remove the frame!)
Hope this helps. It is just basic troubleshooting.
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It's just a SUPER-DUTY Mustang GT Sedan. 198K miles and still rolling HARD.
1997 Crown Victoria P71 SVT *** ex-US Marshall service (the CAR)
STOCK?? I bet it was modified.
13.26 @ 107.24 MPH 1/4 mi w/ me, tools, & full tank of 93 octane
I added CAI, NICHE 19 X 8.5 " wheels with 245/45ZR 19 rubbers, and completely rebuilt the front end with poly bushings, Kooks headers, 2 1/4inch exhaust, TCI 2200-2400 rpm Stall converter
.PLANS:: engine upgrade, 5.4L 2v stroker, rebuild interior in leather w/ buckets, thinking about turbos