Much of the left side of my Big Guns backbox lighting is out. Otherwise, the game plays just fine - all lamps on the PF seem to be functioning without issue.

I tried the obvious first - multiple known-good lamps swapped into each socket. No dice. Then I checked the backbox interconnect board, given its reputation. But continuity tests with my MM across each pin pair, top to bottom, were 100% successful. Is it possible that I could have gotten a false positive? I'm thinking this is a wiring issue. Or perhaps a bad component on a driver board?

You can see in the photo that all of the solid lamps on the left side are out, sans the top left three behind "BIG" (the upper-left most socket works, but needs to be cleaned or replaced as it is intermittent). The strobing gun lamps on the left work fine as well.

What would you all recommend I test next to catch this gremlin?

Also, what's up with this mini driver board on the back of the backbox door? Voltage readings on the labelled leads are much lower than what the labels read at the 28V and 50V pads, but perhaps that's normal?

So I'm getting .6-.7vdc at every single lamp socket, whether it is a working one or not. That seems very odd. Why would they be reading the exact same voltage and yet some of them be working and not others? Is this user error? I've got one of my MM probes on the leads of the sockets and the other on the ground strap. That's correct, yes?

I reseated every connector on the interconnect board. I also checked continuity from the every lamp socket to the pins on the right side of the interconnect for J1 and J3, which appear to be sending power to the lamp circuits that are not working (they are brown, brown-white and orange wires). And everything is testing out perfectly...

What am I missing here, @ericpinballfan, @ltg? Any other tips would be greatly appreciated.

Thanks. That did it. I traced the brown/brown-white circuit, which had zero volts running through it, all the way back to the right side of the backbox, to a blown 5ASB fuse. I swear I tested that fuse before and it was good, but it most certainly was not. Oh, how embarrassing. But I'm glad it was an easy fix.