In the home stretch of getting a Ship Ahoy up and running. Really wanted to get one done without having to ask for help, but I'm good and stumped.

First off - Ship Ahoy is an add-a-ball game. But it uses WOWs instead of having a ball count the can step up and down from 0 to 9. I have it on 5 balls, so at the start of a game you're on ball five and will run through them. When you earn an extra ball, the ball count doesn't actually increase. Instead, a separate stepper increments and you light a WOW on the backglass. You can earn up to 5 WOWs at a time.

If you're on ball three and earn say 3 wows, when you drain, the ball count stepper would remain on ball three and one of your wows would be used up.

The issue I'm having: If I have a single wow - when the ball drains, the wow is taken as expected, BUT it's also then decreasing the ball count. This happens no matter which ball I'm on, and ONLY if I have a single WOW.

There are two earlier threads on pinside that I found describing this exact problem.
In one the issue solved itself via black magic and luck or something:
https://pinside.com/pinball/forum/topic/ship-ahoy-earns-wows-but-no-extra-balls-given
In the other, some in depth posts were made regarding where to look, but there's not really any resolution:
https://pinside.com/pinball/forum/topic/lose-ball-with-wow-lit

Looking at the relevant bit of the schematic - it's pretty clear how things should be working:
schematic (resized).jpg
At the zero position, the 2nd switch on the wow stepper is closed, allowing the ball count stepper to decement on ball drain.
If the wow stepper is at 1 or above, the switch is opened and in theory, the ball count stepper shouldn't be able to activate.

here's some pics of the lightbox advance switch stack in three positions.
0 wows - reset complete.
0-wows (resized).jpg
With 1 wow - where the issue will happen.
1-wow (resized).jpg
With 2 wows - switches the same as with 1, the peg is just further away.
2-wows (resized).jpg

Video of the issue - please ignore my middle aged grunting as I tried to squeeze past a pinball machine in my ktichen.

What seems to be happening is that with a single WOW, as the Wow unit steps down, right at the 2nd switch closes, it's causing the ball count unit to step down as well. I have no idea why though and don't know where else to look. I mention it in the video, but I've adjusted that switch many times - trying to get it just barely closed when the wow unit steps down, leaving it as open as possible when the wow unit is at 1 or above. The ball count keeps stepping down regardless.

Any suggestions?

Bad angle on the photo, but no. Right most switch is open at 1 or greater WOWs.

Opened it up a little more, but still have the issue.
Zero and one WOWs as it is now:
no wows (resized).JPG
one wow (resized).JPG

Uncropped pic of the schematic here:
IMG_8730 (resized).JPG

Blocking the trough switch with paper gets the ball ejected to the lane without losing the WOW or a ball.

Per a message on facebook from another pinsider - with 2+ WOWs, if I hold the trough switch closed, the wow stepper coil energizes but doesn't decrease the WOWs until I release it. At 1 wow - it immediately deletes the WOW and decreases the ball.

Welp - moot point. FB message had included a hunch about what the issue was and they nailed it.

The switch that closes when there's 1+ WOWs wasn't closed hard enough. When the coil pulled in, it was losing contact just enough to cause the issue. Cleaned and adjusted that half of the make/break switch so that it didn't lose contact until the coil released, and it's all good.

Thanks a ton to everyone, AND - if a 4th person has this come up - there's your possible solution.
one-wow (resized).jpg

Never noticed that that was a thing, but done.

Same, more or less. I was told what it might be but it wasn't until I sat there manually stepping down to 0 WOWs that I saw it. Kind of a little lightbulb going off as far as how the stepper was working with that make/break switch. So focused on the 2nd switch from the right that I never would have found it without the suggestion. Feels way better seeing it in action though and understanding why it works now vs. just fixing it.