1) Remove all four of the screws in back of the TremorPak and remove the back of the unit. There is a plastic bar at the top of the back piece, it looks as if there was an original intent to install a feature there-possibly an LED.
2) Remove the two screws to take off the plastic bar at the top of the back case half.
3) Wrap the leads a 5 volt LED around the plastic bar so that the LED is directed forward and the leads do not contact each other. I found that with the LED that I used, the leads were firm enough to hold it in place firmly, but you may need to adhere it with something if your leads are not stiff enough.
4) Solder a wire to each if the LED leads. I would recommend that the LED leads be tinned prior to mounting the LED so that less time and heat around the plastic is needed. The leads still melted slightly into the plastic bar when I did mine, but it probably helps to keep the LED in place when the unit shakes.
5) Solder the two wires to the same two points as the motor's wires. The large element inside the LED is the negative side; connect the corresponding wire to the black motor wire. The smaller element inside of the LED (positive) then is wired to the red motor wire.
6) Reassemble the two case halves being sure to keep the LED wiresclear of the motor's path. I used fairly stiff wires so that they would stay in place.
The LED should now flash whenever the motor is on. I also used nail polish remover to erase the Performance logo from the face of the unit above the LED.
This method should work for other brands and models of rumble packs, but they may not have the convenient bar to mount in to that I was able to use.