Chris, next step is understanding your ZW transformer. Here is the link
. I suggest you print it out.
The very first picture shows the terminals. A U is for the left throttle. The A terminal should go to the center rail. U to the outer.
Now B U terminals are for the switches, B connects to Black, U connects to your button( I think), but it is not needed for auto switching ( which is grounded off the outer rail (U)).
You don't need your voltmeter. You already know that there is not enough power to run the engine and the switch.
The manual may list voltages that you can check to see if your transformer has no problems. They do require servicing. The rollers inside wear out.
Use your volt meter to determine which lead on top connects to black. Connect B to that one. U to the other.
It is great, that you saved the 2023. We encourage everyone to revive old trains. To us they have more sentimental value than anything.
Show and tell us more about you layout when you get a chance.
Being a McGyver, think long term, and look for some used 022 switches, clean them up and replace the Marx switches. They have auto derail, already.