I have a 95 Sc300 with the pioneer stereo. I have been having a very odd problem that occasionally the sound will cut out when the brakes are applied or the turn signal is turned on. it will actually cut out to the same pattern as the turn signal is flashing. Sometimes it just goes out all together until I turn the car off and restart it. It doesn't do this all the time somedays it works perfecty and others it won't work at all. I am replacing the amp and headunit tomorrow to one from a JDM soarer and I hope that will solve this problem too.

 

Check the grounds in the back (any wires bolted to the chassis). Clean them off and make sure they are dry. Also clean your battery terminals.