for a non-tech zippin seems to have a good grasp on how to deal with these trucks
as he said the control handle is pretty straight forward, its mainly mechanical with 2 potentiometers that are usually the problem when things go wrong with the operation of the truck, simply relearning the system or replacing the potentiometers and then relearning the system will fix these issues.

And again on the TMM part, the truck shutting off when you 'tap' on the TMM only tells me there is a connection issue somewhere. Like zippin said, closly check the db connections and make sure they are tightened all the way and you can also remove the TMM and dissassemble it and check for loose connections inside with the ribbon cable connecting the power dist card etc.

But as been said before, if you are not familiar with this truck this will be a learning experience for you (possibly a frustrating one at that) , get the manuals if your plan is to maintain and repair this yourself, they will help somewhat.

good luck