Bottom one is the starter motor safety relay. Cuts the stater motor off when the engine starts. XS2 should have it as well.
View attachment 224256
https://www.xs650.com/threads/72xs2-73tx-wiring-diagram.53244/
This thread may help you. This was a discussion when we reworked an XS2/73TX wiring diagram. Should help with a few questions you might have. 72XS2 and 73TX Electrics shoudl be the same.
The diagram has a Yellow wire going to the brake switches. I'm sure they went to Yellow/Green in the loom to the switches.