[Question] Dual battery issue

Hi all,
I'm having an issue with my dual battery setup. #2 battery voltage drops to 2.5 volts at the terminal block when the ignition key is in the on position.

Here is what I have:
Guest Battery switch set to #1, voltage at the output of the switch 12.7 volts. Turn the ignition to the on position, measure the voltage at the ignition terminal it's 12.7 volt.
Guest Battery switch set to #2, voltage at the output of the switch 12.7 volts. Turn the ignition to the on position, measure the voltage at the ignition terminal its 2.5 volts. Nothing works. Motor wont start, gauges don't come on.

The output of the switch goes to the starter then to the terminal block.

Just doesn't make since to me. The terminal at the starter is the common terminal for the battery switch output, the all 12V goes out from there.

Any thoughts on where I should look?
Thanks,
Jerry

[Question] Dual battery issue