[dmack91]

Next, take out the on/off/volume rheostat knpb assembly. You will.see r small tabs that hold the front and rear parts together. Carefully pry the tabs out, one needs to be heated to release the solder, and pull the two halves apart.

This is the bluetooth Amp I bought off Amazon for $18. You can see the slot in the Amp shaft. Now lightly file the round part of the half circle shaft coming out of the factory on/off/volume rheostat to fit the slot in the Amp volume shaft.