Hi Neil, it depends on the wattage of bulbs etc and battery voltage but approx 12 or 13A on 6v system with everything in use. Fuses have two ratings though, the amount of current they will take continuously and the amount that will blow it, generally about twice as much, so a fuse rated for 10A will blow at around 20A.
I think that bearing that in mind the connector plugs you're using need to be capable of taking a load of at least 15A minimum, if they're the same as I normally use they are rated at 8A (have just been and checked!) which won't be enough!