1988 420 SEL. I just attempted to have a Blaupunkt wired into the factory system by a local shop. They wired the speaker outputs directly into the preamp ins on the factory system because the Blaupunkt pre outs didnt have enough power for the system. This setup Sounds great but when the radio is turned off the internal amp on the Blaupunkt will not turn back on unless the both speaker wires from the blaupunkt are disconnected from the factory preamp ins. This problem does not occur if They use the RCA preamp outs on the blaupunkt but as stated before this does not produce acceptable power.
Anyone have a clue?

Thanks