Can 2 audio head units share speakers?

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.

Nope.  While it is possible for multiple head units to use the same speakers, it requires a switch so that only one can be connected to them at a time.  To do what you require is the reason the adapters exist.Support the12volt.com

So, by using some type of A/B switch for just the speakers work?

Sure it would in theory, but you have to be be flipping the switch at the exact right moment in time that the chime would actually be signalling something. Buy the proper expensive harness and do the job right. Is the wrong part worth a warranty claim on the vehicle that the manufacturer will deny leaving you paying a even more expensive repair bill?Top Secret, I can tell you but then my wife will kill me.