Factory Radio Compatibility

[91lsc]

http://cgi.ebay.com/ebaymotors/ws/eB...tem=2424697051

I put this 94 Mustang factory radio in my 91 Mark Series and have no sound but all other radio functions work as well as the cd controller for the ford/sony 10 disc changer. I have the JBL amp in the car(Dont think it is the ORIGINAL JBL amp) and thought the JBL's for the mark series were all the same. The part # on the amp is E8LF-18B849-BA433M. The part # on the head unit is F4ZF-19B165-BB. Any help would be appriciated. The radios look identical and have all the same plug ins. Technicar in Orlando tech(where all the local new car dealerships send their radio problems) said "this part # of the head unit was compatible with the older amp although the unit had to be fooled to kick out the audio" Thanks, Allan