So I had just fixed the issue of only being able to start a one player game, and remembered I had never installed a remote battery in it. I only had yellow wire with which to make the pack with, so even though I checked to see which was the positive and which was negative, somewhere along the way, I got them mixed up. (I should've marked them, but..) Turned on the power, and the machine went a bit crazy, so I shut it off. I then realized what I had done, and checked the mpu. Saw a resistor right by where the original pack had been that was fried, but everything else seemed ok. It was a 1/4 watt 62ohm, but all I had was a 1/2 watt 68ohm. I figured that was close enough, but now when I power it on, it seems to boot, and the displays light up as normal. I can insert credits, and hear sound. However none of the PF switches or coils are working. When I press start, it acts like the game has started, but the ball does not eject. Where do I need to start looking?

Turned out there was a fuse I missed, which I assume controlled power to the playfield solenoids. Replaced that and all is well!