Ok. Found the 30A fuse for fridge and step. Pulled it. Not blown. Pushed it back in. Step now retracts again with engine start. Fridge still refuses 12V. Fine on gas. Hope it's not a fridge problem as I know Thetford spares are expensive.Model of MH would be a help. If Fiat you should find under the bonnet 3 fuses being fridge, leisure battery and vehicle battery beside 2 relays, the split charge relays. When the engine is started one relay operates the feed to the leisure battery which operates a relay retracting the step. It is this fuse you are looking for. Other makes of MH may operate differently.