Ive had this receiver for a few months in my truck but wasnt using the preamp RCA connections and it works great. I just swapped it into my car that uses the regular speaker connections to drive a few small surrounding  but then uses the pre-amps to drive the main speakers through an amp, nothing is coming from the pre-amps on the stereo. I get sound from the normal harness speaker connections driving the small surround speakers, but nothing from the front and rear preamps. ive tested the rca's on the car side and I can drive them with another source so I know the connections are good and the amp turnon wire is working, and I've connected the stereo to another speaker and no sound. I cant find any settings that turn them on and I cant find any fix, anyone know whats going on?