adding a relay will protect your system from overload
that being said you must tap into your parking light wire from your master switch, if you can find the wire in the loom of 453286 wires u can tap there too
for the amperage, it all depends on the Led lights...assuming they only draw minimum watts, you would not need a high amp fuse, however to be safe use a 30 amp fuse
bill kemp has a link which shows the formula to calculate watts and amps, it also shows the amount of wire in feet and what guage you should use...
a relay is a very simple unit
it has two independent circuits inside...an electormagnet from one (your parking light wire +) would connect your clearance lights when your parking lights were turned on....
a relay has 4 posts 30 87 85 86
30 and 87 are for your clearnce lights
85 and 86 are your parking light + and a ground
30 draws a 12v power source direct from your battery
87 is the wire that feeds your leds
the fuse would go between 30 and the battery