The PS-1 system is designed to run with an 8.4 volt Ni Cad rechargeable. If you hook a regular alkaline to it the board will try to charge it and it may explode, making a huge mess. You can use a 9 volt Li-Ion rechargeable. I am guessing since you plugged the tender into the engine and it ran, both are PS-1 so that is good. In order to make sound that speaker needs to be plugged into the board. There is a 2 pin plug for the speaker, it may be marked. If not someone can chime in with the correct plug location. As I recall the pot you need (for sound volume) is a 10 K ohm. Any 10 K pot will do. It will not likely make sound without the pot. The 4 wire tether uses 2 wires to supply AC power to the board from the engine, and 2 wires to supply DC back to the motor for movement. I forget the colors, but no matter if it already moves. You may be able to order the correct PS-1 chip from MTH to get the correct challenger sound file, not sure. Last time I checked they still had lots of various PS-1 chips. This engine is pre-command era, meaning it responds to variable AC to the track for speed, and power interruption results in direction cycling.
Hope that helps,
Rpd
