This issue started with Frodo/Mode Start activating automatically at the beginning of a game before the first plunge. I found some posts indicating that it was likely an issue with breaks in the Balrog wiring harness. Got a brand new harness, replaced the old one.

Now, when the game powers on but BEFORE starting a game, a ball is ejected and is auto-launched, then a second ball is ejected and auto-launched. Once the first ball makes it back to the trough, another ball is ejected and auto-launched. Always two balls forced out of the trough.

This seemed like an issue distinct from the Balrog, but unplugging the Balrog prevents this from happening and a game can start normally.

I've since replaced the Balrog switch and diode, but still seeing the strange behavior when the game powers on.

Any ideas?

Plugged in the switch sans balrog mold. When the switch is closed, as it is by default when it's sitting in the Balrog, these switches are active:

4-BALL TROUGH #1 (LEFT) - #11
4-BALL TROUGH #2 - #12
4-BALL TROUGH #3 - #13
4-BALL TROUGH VUK OPTO - #14
4-BALL STACKING OPTO - #15
BALROG HIT - #28
BALROG OPEN - #31

When the switch is open, these switches are active:

4-BALL TROUGH #1 (LEFT) - #11
4-BALL TROUGH #2 - #12
4-BALL TROUGH #3 - #13
4-BALL TROUGH VUK OPTO - #14
BALROG OPEN - #31

So, closing the Balrog switch is activating the 4-Ball Stacking Opto, which is causing the constant ball launch.

I've completely replaced the Balrog switch and diode since taking the picture I included in my above post, but still seeing the same behavior.

Turns out this was a simple and easily avoidable mistake. Compared the wiring to other switches under the playfield and found that the white wire was attached to the wrong lug.