Here is the diagram for ST Prem Flippers. There is a misprint in manual calling out two Upper Left flippers, so not sure which one is the right. You'll have to determine by wire color at the fuse...GRY-YEL or BLU-YEL.
Try this: Power off of machine, replace fuse, remove connector J9 from board. Meter on Ohms/Continuity. Black lead on Ground Strap. Red lead on either end of GOOD fuse, do you read a short or 0 ohms? If not, then replace J9 and do the same test. Now do you read short or 0 ohms?
As a comparison, do the same tests on a working flipper to see if they are different readings.
Also, you can check the coil itself....remove the fuse and J9, meter on ohms, and measure the resistance across the two coil lugs. Compare to a working flipper (don't forget to remove fuse for the working flipper).