After many hours of head scratching and trying to clean very small contacts, without success, I decided to ditch the PCB and small contacts that thetford want £50+ to replace!
First check you have 12v power to your pump by removing the small two wire contact from the PCB and contact the + and - wires to a suitable 12v supply and listen for the pump operation.(if this does not work the you need to look at your pump in case it is seized).
Next establish if you have a live circuit by using a multimeter across the red and black wires on the large PCB connecter these should show 12v (these should be the pair at the red wire end) if no circuit detected, check the fuses.
All being well, them make a small panel out of thin rigid white plastic to fit into the recess on the top of the flush tank.(use the stick on label as a template).
drill a small hole each end of the panel. and a larger hole in the centre to take a small push switch (I got a small horn button from Halfords £8 )
Now all that is needed is to ditch the PCB and the holder which will leave adequate space for wires etc, connect the two black wires together and run the two red wires through the switch. and then screw the panel into the top of the flush tank recess with two small round headed screws. or use tape if you would rather
no more problems with corroded contacts. the only downside with this method is that the red tank full light will not work. so just look down the hole. Good luck
I can't see a way to add photo
Yes the C250 is prone to corrosion of the fuse and its terminals, the level indicator pcb tracks and connector and the main pcb tracks and its unobtainable connector under the flush button. Had problems with all of these and replaced all too..