Truck is taken apart right NOW... need help from audio people

delete

 

You can't connect one speaker to two radios/amplifiers.
When you power on the HAM, the OEM radio sees a short in the speaker system and shuts down.
Install a seperate speaker for the HAM. Or look into getting a isolation box that allows two inputs to one speaker. Expensive and complicated for the simple setup you want to do.

Fritz

 

You need a means of switching the wires from the stock radio and the wires from the ham radio so that only one radio is hooked to that speaker at a time. A double pole double throw toggle switch would do the job. Should be able to get one at napa, radioshack, home depot, etc. Just have to route all the wires to the location where you put the switch.

I've never experienced this myself, but I have been told that most stereos are "smart" enough to shut them selves down if they detect a backfeed into the speaker wires.

Edit: Using a toggle switch isn't going to work if your goal is to have the stereo cut out automatically when you recieve a radio transmission on your ham radio.