There are three I/O boards in an I-game. The one in the door with a 96 pin wide connector handles the lower row of switches/lights, coin-in, and a few other things. The one in the cabinet on the left with a 48 pin narrow connector handles the meters, candle, and a few other things. The I/O card on the right with the 96 pin wide connector handles the upper row of buttons/lights. All of them communicate with the MPU board via over the same serial network (SENET) bus.
So if you have Meter's disconnected and Coin-in Jam errors, which I know you do, the following could be the cause.
Bad MPU board,
Two bad I/O boards, the one in the door for the Coin-in Jam, and the one the left hand side inside the cabinet for the meter's disconnected error. (Not likely)
One I/O boards is bad effecting the SENET bus so that the MPU can't communicate with the I/O boards.
You can check to see if one of the I/O boards is causing a SENET bus problem by pulling it out and powering up the machine. Say you pull the one in the door, power up the machine, and now you only have a coin-in jam error. Then that board is likely the problem as the MPU can communicate with the cabinet I/O board and see the meters are connected again. If you still have both errors, plug the board back in and try the one on the left inside the cabinet. If the Coin-in jam clears, but meters disconnected stays, then then one probably bad. If you pull the I/O board on the right then both errors should clear if it is bad, and the game will play, but the upper button deck will not work.
If it's none of the IO boards then it's the MPU board, or a broken/cut/shorted wire somewhere, or possibly a bad motherboard connector/pin.
Do not remove or replace any of the boards with the power on or you will create more problems.