Just r/r the radio in my 740...I figured out that the front speakers on the dash
were driven by the radio itself and the rear doors by an amplifier located underneath. What was interesting was that the front doors had prewiring for speakers and was connected to the enderdash amplfier.So in all 12 wires to the
underdash connector 2 blacks/2green-red...corresponding to 2 grounds and 2 +12v
independent of ignition switch...I was told amp was a 2 stage amp hence twin power????....the other 8 wires were speaker . The harness by the radio had 4 wires for the dash speakers ,a green for the antenna ( yes green...not blue
as I had expected), yellow ,black ,green-red and blue.After the installation
the only thing I didnt have was the ability to vary the lights in the radio with the dash control. The antenna bypass worked also.To retro fit I needed
METRA part no.99-9222 for the dash and for the harness pt no. 70-1120.
The harness part was hard to find so I hard wire all my wiring with a solder gun
and heat shrinking tube for insulation. No need for antenna extension!
Total cost for installation....under $20!!!!!regards.