if the voltage to the lamps are correct then it could be:
A: Some of the G.I. wires have been wired incorrectly (wires on the plugs that go to playfield and back box G.I.s) and there are more lamps on one or more of the circuits than there should be. (hot plugs)
B: Bad solder joints on fuses, Faulty fuse holder or faulty fuses. (hot fuses)
C: when the new plugs were installed the pins in the housings were not crimped properly, or the headers were not changed or the headers were not soldered in correctly (hot plugs)

You will need to check if the wires were fitted in the correct positions when the plugs were changed. If all the wires are correct and the voltage is correct it comes down to faulty parts / or workman ship.

I have just recently fixed a wpc driver board with a burnt G.I fuse holder, all the plugs and wires showed no signs of heat stress, it just came down to either a faulty fuse, fuse holder or bad solder joint.