Thetford C4 Toilet no power to pump

Hi I have just got my hands on Libby our latest camper, the problem is this: as it stands the 3a fuse was blown, replaced then tried flushing no go but fuse did not blow, Lights on and again no dimming and no noises. Removed pump from under toilet roll holder and it had been replaced before and water had got into the wires. Pump itself was seized up so played around and oiled it and tested on battery works a treat. Put pump back on system and nothing.... over to the experts