If you read both of those sys1 wiki's, there are some processes to verify power.
You'll want to unplug J1 off the power supply board, and test the power at that plug. Then when verified good. Unplug J2 and J3, plug in J1 to power supply board, and verify voltage at those J2 and J3 pins.
The interconnect harness is the plug between the mpu/cpu and the driver board.
What I started to realize is these old games have soooo many issues with pin corrosion (and bally/sterns) that repinning all connectors is just a tedious but great way to skip any weird issues that those may bring.
As for the fuse on the small transformer. It is recommended to install 3, the one you have is the stock one, but doesn't protect the other two power lines
220.127.116.11 Recommended Fuses to Install to Protect the Small Transformer
It is recommended to install three fuse holders to protect the small transformer from potential shorts.
110v/115v/120v: These lugs are the incoming voltage to the small transformer (for US games, it should be 115v). It should have a 1 Amp fuse. On earlier games, this fuse is missing, so it will need to be added. Gottlieb included it starting with Solar Ride and all later System 1 games. However, it's possible that someone may have swapped in a transformer panel from an older game into a newer game, so in that situation, the fuse could still be missing in a later game.
Lug 6: This is the outgoing voltage to the power supply for 11.5 VAC. It should have a 2 Amp fuse. This ultimately becomes +5VDC, when rectified and regulated by the power supply. It passes through CR1 & CR2 on the power supply.
Lug 7: This is the outgoing voltage to the power supply for 14 VAC. It should have a 3/4 Amp fuse. This ultimately becomes -12VDC, when rectified and regulated by the power supply. It passes through CR3 & CR4 on the power supply.
Desolder the wire from the transformer lug. Position a fuse holder (such as a Bussmann / Eaton BK/S-8002-1-R with solder lugs), make sure the desoldered wire will comfortably reach one of the lugs, screw down the fuse holder (a #6 3/8" or 1/2" wood screw), then solder the wire. Cut a piece of wire (about 5" in length) to connect the other end of the fuse holder to the appropriate transformer lug. For lugs 6 & 7, use 18awg wire. For the incoming voltage, use 16awg wire. Strip and solder the wires to the appropriate fuses and transformer lugs.
When done, install the fuses, and with a multimeter, perform continuity tests from the original wire to the transformer lug. As a safety measure to protect the electronics before turning on the game, disconnect the power supply, MPU, driver board, and sound board (if applicable). Then, turn on the power, and use a multimeter to test the voltages to ensure the voltages are correct and going to the right connector pins.
Lastly, be sure to add labels for each fuse holder to indicate what the type and value of each installed fuse needs to be.