I think this is a pretty generic lamp matrix issue, so I haven't specified a game in the title, but I'm working on a Sacred Stiff. Here's the deal... Lamp 32 (Crate Center Left) always lights with any other lamp in column 3. There are no other problems, specifically, all other lamps in row 2 work fine. Does this suggest lamp 32 is shorted to ground and any time column 3 is energized it fires regardless of the signal present in row 2? If so should I test out that LED board somehow? Possibly the connector or Red-Black wire that's for row 2. Thanks, this is probably a slam dunk for most of you guys.

Good idea. I pulled the cover off the crate and all the the board-mounted diodes on the crate LED board test fine.

Sorry, I don't know what that means. I haven't pulled the power driver board and tested Q95 (column 3) or Q108 (row 2) as I'm having a hard time working through the logic of how if either of those shorted would result in the phenomenon I'm seeing. To me it makes more sense that whenever column 3 is energized and if red-black for row 2 is closed to ground that lamp 32 would always light. Testing at the connector pins on the crate LED board does not show any continuity to ground.

OK, here's the update and it's crazy. First to reset something from the original post, although in the grand scheme of things it's irrelevant. The lamp that was always lighting in column 3 was #33 (Crate Center Right) anytime another lamp form that column was on.

Anyway, I decided to test the diodes in the row associated with the wonky lamp. So, as I'm working through row 3 I come to one that tests bad, on lamp 62 (Skull Award). Thinking I'm all set I replace it and this one also tests bad. Not that's unexpected. For some reason I decide to take the bulb out of the socket, sure enough the diode now tests good. All too weird for my liking, so I stop and think for a second. The "Skull Award" lamp also fires the eyes in the skull pile mod I installed years ago. Disconnect the two connectors from that and all is well. Right now I have no idea what to make of that as I haven't dug into it yet. If memory serves the wiring for these was already in place, but the feature was removed of production. I'm not even sure if I can find references for that wiring. I need to research, but I wanted to call you guys off from trying to figure out a "common" problem as this is probably quite unique.

Thanks to everyone who's been helping. If by chance you have any ideas related to this I'd love to hear them otherwise I'll report back if I track down the issue.

This one has me stumped. Quick recap... Lamp 33 (Yel/Org-Red/Org) lights anytime any lamp in column 3 (Yel/Org) is fired. This only happens then the lighted skull pile mod is connected. The diode at lamp 63 (Yel/Blu-Red/Org) tests bad only when both connectors for the skull pile and the bulb is in the socket at position 63. FYI, the skull pile mod was purchased (can't remember where), not a DIY.

The wiring for the skull pile looks correct and it works fine during game play. There are two connectors for the skull pile. The yellow connector connects to Yel/Grn and Yel/Blu game wiring. Strangely when just this connector (not the red one too) is connected the lower left skull (Yel/Grn-Red/Org) lights solid in attract mode. That seems weird as only yellow game wiring is in place. I don't think there should be any path to ground. The Red connector connects to Red/Org, Red/Blk and Red/Brn game wiring. When only the red connector is connected the top (Yel/Blu-Red/Blk) and middle right (Yel/Blu-Red/Brn) skulls light in a cyclical fashion in attract mode. Same question about how the red connector alone is able to complete a circuit. At this point I'm wondering where the "unused" skull pile connectors are connected to the power driver board. Maybe something is wrong there, but it's not a problem until something is actually connected at the playfield end.

***Solved***

For whatever reason whoever manufactured the skull pile did not include diodes on the LED pairs. Pretty frustrating, but easy enough to fix. Once those were added everything worked just as it should. Primary lesson I learned was diode problems (or omissions) can cause all kinds of weirdness and make diagnosis tricky. Make sure they are present, wired correctly and functional else true solutions will be particularly be elusive. Thanks to everyone who helped or followed along.