...damage to either unit? I have a 2003 Sierra with a stock am/fm radio with RDS that uses the speaker system to transmit information signals, like a chime tone when the fuel is low. Aftermarket head units would require an expensive special adapter to connect if I want to retain that function. Couldn’t I just install another head unit with a CD player in the truck, and share the stock speaker system? I am concerned if feedback from one unit to the other could cause damage or other problems.