I'm posting this for future troubleshooting - I've fixed the issue but it was an odd issue. On my Jungle Lord, Williams System 7, when a game was started but pushing the start button, it would score 10,000 points and drop the middle drop target on the upper playfield. I figured I had a short or bad diode on one of those switches. The diodes tested fine so I put the game in test mode and got to the switch test.

On the switch test, closing the switch for the start button caused all the switches in that row to close. The start button is a "column 1" switch. I then noticed that all of the column 1 switches caused their associated row to show closed as well. All other switches not in column 1 worked just fine.

I then went to the driver board to test the columns with my voltmeter and found the columns were putting out ~4.7 volts dc, but nothing on column 1 (pin 9). I figured a bad 7406 inverter chip I17, so I replaced that and checked the associated resistor/jumper/capacitor and they tested fine, but the issue persisted. Using the diode function on my DMM, I started checking the PIA chip and found the pin associated with column 1 measured ~20% higher than adjacent pins, so I replaced the 6820 PIA chip and now everything works fine. A bit odd, most of the PIA chip issues I run into cause the CPU board to not boot up at all.