To start, I would make one of the circuit breakers w/fuse so you don’t keep wasting fuses while you track down the short. As Jrpinball suggested, look at your work. Possible tab on socket bent over causing short. I don’t have time to find information on making the circuit breaker at the moment, but look on Clays pinball repair site as I think it’s there.

Here ya’ go:

When diagnosing an EM that always blows a fuse, using a circuit breaker instead of a fuse is mandatory! (Unless you like spending extra money on fuses.) I make the breaker easy-to-use by soldering a blown fuse to a small PC board circuit breaker. Breakers are available from lots of places like Mouser part# 655-W57-XB7A4A10-5 (Tyco 5amp breaker) and 655-W57-XB7A4A10-10 (Tyco 10amp breaker). I like the Tyco W57-XB7A4A10-5 as it's a good quality and size, with a low $2 price. The Tyco breakers don't come smaller than 5 amp, so if you want some smaller breakers for solid state pinball work (recommended) check out SMCelectronics.com.

After getting the proper breaker, just solder a blown glass fuse to the breaker's terminals (and use some silicon to help hold the fuse in place and to prevent the glass tube from breaking).

For EM work, a 5 amp circuit breaker is perfect. (I use 5 amp circuit breakers for the main EM solenoid and light fuses.) Anything below 3 amps will be too low for the solenoid circuit on a typical EM game for more than a couple seconds (mostly because the score motor consumes the most power, as coils are only "on" for just a moment). Remember circuit breakers don't blow as fast as a fuse, so you want to use a breaker that is lower amperage than the fuse it is replacing, which in most EM games will be 10 amps. It takes too long for a 10amp circuit breaker to blow in a game, so I generally don't use a 10 amp circuit breaker for too much (though the 10 amp does work well after you have the game all done, if you're out of fuses!) Better to use a circuit breaker that is too low in amperage, than too high, when trying to diagnose a problem.

Here's a circuit breaker I modified with a blown fuse soldered to its lugs.
Why the blown fuse? Because it makes installing the circuit breaker into a
fuse holder a breeze!