Continuing problems with Thetford toilet

When we first used our new Thetford toilet in our 2009 3124KB, it didn't work properly...even one sheet of tp did not flush down. We contacted Thetford, and the local rep, and he replaced the pump, saying the toilet now worked. When we went out again for 10 days, it was obvious that the toilet did not work any better than with the first pump. There is not enough force to the flow of "water" and it comes out only from the back and part of the back left side. Finally today, Chris found someone at Thetford who seemed to have an idea what might be wrong. He said that our symptoms were the same as if the wires to the pump were hooked up backwards. Now here is the question? Do you all think we can change the wiring ourselves? Our local rep is obviously a hack and the nearest place that might repair the problem doesn't do warranty work and charges 140/hour, and we don't have much confidence in them. We have no wiring diagrams and don't even know if we can easily reach the wiring. BTW the good guy at Thetford said the pump would run if the wiring was backwards, just not run properly. Thanks for your help....