You don't say what unit you have but lets assume you have one out of the Thetford range. The Thetford web site has PDF drawings of their units to allow users to identify various part numbers they may want to order but the same drawings can give you an insite as to the location of any switches, relays or wiring harness. It also gives you a good idea as to how to strip them down
So go to: www.thetford-europe.com
Then,
Home page. Select English
Select customer service (top line)
Select products from top line
Select built in or portable which ever applies.
Select user information from list on right.
Select repair instructions from list on right
Select built in or portable which ever applies.
Select your toilet series model number from right list.
You will now be in the pdf listings for your range of toilets just select those that apply to your toilet and down load them they're free.
As you go through watch for 'ask Thetford' on left listings
you may not find what you want and you can send them a message.
Good Luck
CC Member 18017873, August 2012