Electrics

Hi All,
I have a 2004 Swift Lifestyle motorhome. I've had an issue with the Omnistep not retracting on start up, the fridge on 12v whilst travelling and also the mcb has been tripping for the fridge,water heater,battery charger mains circuit. There are three fuses under the bonnet with the relays controlling the 12 volt cut out when the engine is running and step retraction and 12 volt fridge operation. The (cheap) 15 Amp fuse had melted and on replacement everything was working fine. Could anybody tell me where I could find a wiring diagram or shed some light on how the 12 volt and 240 volt systems are connected. What Amperage should the 3 fuses be and which protects which circuit ?
Thank you all in anticipation of your replies.
Richard

Moderator Comment - Please see post in the Motorhome section, I have locked this one to avoid duplication