Open your manual to page 1-13 and perform switch tests. You'll find one or more of them not registering properly.

Odds are whatever switch is associated with Rats and one of your trough switches isn't working. There could be a variety of reasons for that. Let's start by figuring out which one(s) are malfunctioning.

Welcome to Pinside!

BSDSwitchMatrix (resized).png

In the switch test, with four balls in the game we're looking for switches 41-44 to be closed. This will tell us that those four switches recognize that a ball is present.

Bear in mind that during play one of the four balls gets loaded into the Myst area so it's normal to see three trough switches closed and either switch 61 or 63 closed because the Myst ball should be in one of those locations.

For testing you can use another ball or take the Myst ball out and use that one.

If you want to take a photo of the switch edge test and post it maybe we can help explain what it's telling you.
https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Built-in_Switch_Testing

When you took that photo, where were the balls?
Four in the trough?
or
Three in the trough, one in a Myst lock?

I -think- Bram Stoker's Dracula kicks out balls from the coffin lock at the end of a game but I'm not 100% sure.

I'm assuming you mean switches 51 and 53?
Switches 61-63 are for the Jet Bumpers.

Oooops. I meant 81 or 83, thinking that the Myst ball would be in one of those positions. But the switch matrix doesn't show those as optos. Treelk 's photo does show 83 closed though so that's probably the Myst ball.
Thank you for catching my mistake.

Ok. Let's go over what this picture shows us. Back in post 2 or inside the back cover of your manual we see the switch matrix chart. The left side shows a column of dedicated grounded switches. Those are represented in the photo as the eight dots on the left side. A dot means the switch is "open". All is well so far since we expect all of those switches to be open.

The first closed switch is in column 2, row 4. It's represented in the photo by a box. Looking at the switch matrix that's number 24 "Always Closed". So far, so good.

The next closed switches are column 4, rows 1&2. Switches 41 &42 are Trough 1 ball and Trough 2 ball and you said you had two in the trough so that looks right.

Column 5, rows 1-7 are opto switches. They are normally closed and in your photo they show as boxes so those appear to be working.

Column 7, rows 1-3 all show as closed in the photo. The matrix lists those as optos - but wait!

Ahha! An anomaly.
When an opto switch is blocked by a ball it should show as open and look like a dot. You should be able to test that at the left ramp entry. Block that with your finger or a ball and switch 73 should change state.
Switch 71 should show open if there is a ball present. It shows as closed in the photo. So check that opto.
Could need cleaning, could have a bad transmitter or receiver, or could be mis-aligned.

I suggest you pull out all the balls and see if you can get that switch to register consistently. You might try using your phone on video setting, I think you can see if a transmitter is working like that.

Let us know if you have more questions or need more help.

BSDswitchstatus (resized).png

One thing I can't tell is where does the ball go when you hit the Rats shot? Is there a subway that takes it over to the Castle Popper? That might explain why Rats isn't working either.

There is one connector under the playfield for all three of the castle lock switches. If none of them work in switch edges test (run a ball thru or use your finger), follow the wires under the playfield to that connector and make sure it's not unplugged. If it is unplugged, the other end should be nearby and wire colors should match up.

While you're in your switch edges test and you put a ball in rats does any switch activate?

Ha, you have been saying bats the whole time and my mind went to rats way back in post two and I never noticed.
What is the bats shot? Left ramp? If so, what about switch 73, the left ramp entry opto? Check that one.