hi
if you put the battery under the pasenger seat (make sure you secure it properly
) and then you can run the cables through a rubber gromet(put your hand under the carpet or look under the vehicle )
to conect direct onto your main vehicle battery + and the - can be picked up from any bolt around
for the swiching of the relay this could be taken from left hand side of the glove box , remove the side cover that has a cup holder in it and you will see the fues box - remove the t20 tourx screws and pull(push the lip of the front fuse box up)
the fuse box from behinde be carefull of the cables or if not to confident with doing this you may be able to conect onto an igniton live from underneath hope this helps you ?
regards
darren
AOC