They can be a pain in the a**.
I've seen the fuses, in the plug, accessed in a couple of different ways. The most recent involved little doors, on the outside edges. The door slides up to reveal the fuse......one on each side of the plug.
The other, you need to squeeze the plug blades together and pull. You can usually tell that they have line or cut around the bottom (blade end) of the plug. You should have to pry gently if it has the little doors.
I know what you are going through, I've got a bunch of light sets that I just can't bring myself to fool with.
Good luck, keep us posted as to your progress
Central Wisconsin's most fun guy! Handy member since 3/14/'94