Do you have the manual and schematics. There is a table somewhere that tells you what the colour code numbers are... red with two greys may be for example 388 ... you find out what the number code is for that wire then find it in the schematic.

For the sound card I don’t think the mpu can ‘sense’ a problem with the card and do something to the solenoids. I have a paragon with same sound card. I’ve only found that the mpu doesn’t boot up if the card is disconnected.

That said, the sound card and solenoids use the same address bus. (Ie...sound card play this note or solenoid card fire this coil. If there is a problem with the select line between the two it may trigger something on your solenoids when it tries to send a tune to the soundcard. Anyone ever seen that?

From HGT manual
Red grey is 19

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yup... sounds correct. I couldn't find a 19 anywhere on the schematics. 13 (red yellow) or 14 (red green) on the schematics for tilt and slam switches. There's two red/green wires because one continues on to the Credit Reset per the diagram. Quench's wire is the one on the bottom right. The diode is CR10 that you're connecting it to.

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It's been a while since I was goofing with my soundcard (separate thread). I thought it didn't boot when I disconnected it, but in hindsight I don't recall if I actually played the game when the soundcard was pulled.... maybe I just thought it wasn't booting up 'cause I didn't hear the ditty tune after booting... d'oh! .

Select line is from the MPU to both the SoundCard and the Solenoid drivers. Here are the places in the schematic (and check the wiring harness page to find the colors of wires etc...). First is where it comes off the MPU, second is solenoid card, third is sound card. Per RoyGBev's recommendation disconnect the soundcard connector when you are debugging the solenoid driver.

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Can you force a Special and see if the bank resets when the knocker goes off? The two wires could be shorted and both are firing when either of them do.

Concur with Quench... signals are not going low enough... but if it's all of them it could mean the whole board isn't grounded ... or if the grounds on the SCRs end up on a common track that gets cut before it gets to the edge connector ground pins?

...or the pin 12's on U1,2,3,4 share a trace that doesn't get back to ground?

If it's the whole board and TP2 is not zero volts, you could try to ground the whole board by putting a jumper on TP2 to a known good ground on another board.