Thank you SAXONDOG! One of the RX-18 details you posted showed what the three wires going to the volume knob are. I hooked the right two together eliminating sond control and the sound works. Clearly shows that the volume control has gone bad. Did switch the motor plugs and solved the steering issue. Thanks to all who offered ideas and suggestions. I am back at getting "killed" by my 11 year old who is much better at tank battling than I.
The only question is what to do next!

Thanks again!