Open door, remove toilet cassette unit, look in under flush water tank, observe a short metal blade that actuates a safety switch. This is between two plastic guides. Now look just outside the right hand guide. There you will find the fuse which is a standard blade type. Just pull it down to remove from holder. You will probably find it rated at 3 amp. If it is blown you will probably have to replace pump. Looks difficult but is actually dead easy. Instructions come with replacement Thetford pump. Only problem you may have is a perished sealing ring on the paper holder cup which is no longer available as a spare. Just use a good quality outdoor type sealant as a replacement. Be sure to recover any bits of broken ring from the flush water tank as these can be drawn into your replacement pump and cause it to sieze. At minimum this will cause you to say bother!

Happy repairing.