There are several books that might fit your needs...
RV Owners Handbook includes sections on general repairs, driving and towing, winterizing, electrical, plumbing, heating and cooling systems.
RV Repair and Maintenance Manual covers a broad range of subjects including electronic circuit boards, brakes, 110 and 12 volt electrical systems, plumbing, and heating systems.
RV Electrical Systems covers everything you need to know about your RV's 12 and 110 volt electrical wiring and systems. Includes troubleshooting.
Trailer Life RV Maintenance is an oldie but a goodie. This book is a good reference for basic understanding of RV system design.
The RV Handbook - This handbook tells how to buy, maintain, and get the most from your RV.
The above books are available through online sources like Amazon.com, or
RV Camping Books and Maps