Probable a bad connection on a terminal block in the wiring to the toilet I take it you've tested the current to pump when depressing the flush switch? Another camper had same prob his dropped to 4volts and what he found behind the bathroom panel a bad block joint re-did joint all ok.
www.thetford-europe.com or www.thetford.com.au Australian campers. follow this. for repair downloads.
HOME PAGE SELECT ENGLISH
NEXT PAGE SELECT CUSTOMER SERVICE (tope line)
NEXT PAGE SELECT USER INFORMATION (left of pic)
NEXT PAGE SELECT REPAIR INSTRUCTIONS (left of pic)
NEXT PAGE SELECT BUILT IN TOILETS [top right of pic]
NEXT PAGE SELECT C2, C3., C4 (or relevant) or select your model
NEXT PAGE PDF Files YOU ARE NOW IN PDF FILE LIST
bob, March 2009