Here's a picture from a FPII
Basically, you take 1 AC lead from each bridge - whichever one doesn't matter - cut it, and solder a fuse holder in
1 bridge has blue A/C leads, the other has red ones - again, each bridge has *2* a/c leads, only need to fuse one.
Then, put in a 8 amp slo blow fuse for each holder.
Now, why do we do this?
WMS had a flawed design that they fixed around F-14 tomcat. If either bridge or the big blue cap shorts in the backbox, it could start a fire. I've never fixed one that burned, but I *have* fixed a couple where the bridges shorted and melted the wiring clear back to the transformer!
Cheap insurance.