before you do anything. go turn your other three way to the landing light and see if you can come back to the landing switch and then turn it on.
I agree - but that's how it was when I took the panel off. My next step is to remove one wire at a time from that screw and see what it does.There is no way that there should be three wires on the gold screw of the three way switch. Remove them all and put them back one at a time until you figure out which one belongs there.