I believe Jeff did the wiring instructions for this but it is on the forum that dare not speak it's name.
go here this should helphttp://www.kampenwagen.co.uk/split%20charge%20relay.htm
Go to your local radio-stereo shop and enquire about split charging your vehicle or even halfords,you`ll find they will do it for You cheap enough.If not look in yellow pages and find an auto electrician,they`ll come to your house and do it for you.