Around the time the twin-cams were coming out, HD came out with a Dealer installed upgrade for Ultras and Tour Pack equiped Classics using the sidecar (two channel) amplifier (HD # 76218-98) to boost the power to the rear seat-pod speakers. My bike has the upgrade and I have every installation sheet for my bike except the one for the amp. I've looked everywhere and have decided they must not have given it to me. I want to replace it with a four channel unit so I can run the fronts, rear pods and saddle bag speakers when the tour pack is on and the fronts and saddle bags when it isn't but have no idea how to retain the functions of the rear seat controls without a wiring diagram. I understand I won't have this function when the tour pack is off. Does anyone have the instruction sheet for the upgrade? The Repair Manual shows sidecar wiring but the sidecar speakers are not controlled by the rear seat controls and the amp only powers the sidecar speakers.