You can download the owner manual that includes the wiring diagram fromhttps://lookup3.toro.com/request/request.cfm
Enter your 73400 model number and select "Riding Mowers" for the product type. Next page scroll down till you get to 1993. There are other manuals there also that are a free download.
With the pto OFF one switch has a set of contacts that are connected (switch closed) - this is where the Purple and Tan wires go. The other switch has a set of contacts that are disconnected (switch open) - that is where the Orange and Dark Blue wires go.
With the pto ON the Purple and Tan wires are disconnected (switch open) and the Orange and Dark Blue wires are connected (switch closed).
Got a camera but no matching tractor to use it on.