Hello, my name is Rusty. You don't need an amplifier, it's built into the system. Let's find out what's going on.
Switch the left speaker wire with the right speaker wire on the back of the unit. Which speaker comes on now?
This will tell us whether it's a speaker or an amp. If it switches sides, you have a dead right side amplifier. If the problem remains on the same side, your right speaker has a problem. Tell me what you find.