After reassembling the left flipper, its fuse blows right away. With the fuse blown, the flipper button also stops showing up in switch test.

Flipper blows its fuse after a rebuild: diodes shorted by reversed power wires

Cause: The power wires had been put on the wrong lugs for a moment, which shorted the coil diodes. On these pre-Fliptronics games the flipper button is sensed through an opto-isolator fed by the flipper power, so no fuse means no switch reading; that part is normal.

Checks

• Check the wiring: the lug with two coil wires and the banded ends of the diodes takes the power wire; the center lug (thick wire only) takes one EOS lead; the lug with only the thin wire takes the other EOS lead and the flipper switch wire.
• With the power wire off, measure the coil: about 4.7 ohms with EOS closed and about 160 ohms with it open. A reading near 1 ohm points to shorted diodes; clip them and measure again.

Fix

• Fit new diodes (1N4004 or 1N4007) on the original coil if it measures correctly.

Systems

• WPC Alpha-Numeric

Games

• The Machine: Bride of Pinbot

Related tips

• Game locks up or behaves strangely, worst in multiball
• Isolating the 50 V flasher circuits for LED flashers
• Mount the flipper coil with its lugs away from the coil stop
• Flipper rebuild step 1: remove and check the coil stop
• Flipper button registers but the flipper does not move
• Flipper rebuild step 2-4: pawl off, check bracket and rubber stop
• Flipper buttons not seen by the game (pre-Fliptronics)
• Bride of Pinbot shows the wrong face

Source: Pinball Repair help group!! (Facebook group)