if your only going to run a sat nav off it get a cheap 12v extension socket
wire it directly to the battery or solder it to the fuse box live supply via a fuse say 3A that should work fine tuck it into the glove box when not in use ..
Thank for all the advice, however i have no idea how to do anything like this, i just wanted to take it somewhere so someone else could do it for me, but for cheap!
So if i take it to a garage and tell them i want it doing like above, do you reckon they will do it for me for decent price if i got the parts from maplin?
I wish i could do it myself but its not going to happen!
Thanks for all the advice, at least i kinda know what i'm looking to get done.