It could be a bad bulb or socket.
Lift playfield and unscrew all of the GI sockets on that string. (It is easier to work from the underside rather than having to remove topside playfield toys/plastics to get to the GI bulbs.)
Remove all bulbs on that string.
Put new fuse in and then replace bulbs one at a time until fuse blows.
I usually keep a box of 100 el cheapo Chinese fuses on hand for when something like this happens. Once the short is located and fixed I put a new proper rating and type fuse back in.
