Just to share a fix with my starter relay switch activated with the brake caliper.
I had this problem before so knew where to check for it.
Once the housing is off, the caliper switch needs to be unscrewed as a unit (wires attached) from the frame revealing the push button on the end.
I found it to be stuck in the pushed-in position which is the "off" one.*
A little WD 40 and it was freed to pop out to the "on" one.
Pumped it a few times so it moved freely and put everything back together, this time reverse-twisting the wiring beforehand so it would not bind when screwed in. Bike started OK; easy fix.
My point is that when a button switches like that seizes up it will be in the "off" mode, thus no start. Lubrication fixes it, allowing it to spring out when the caliper is pulled.
*opposite to push-for-on which one might assume
For what it's worth...