Are they GI? My embryon ones only come on at certain stages of game play, I don't know xenon though. If they are controlled, do these have a lamp driver? If so that's where I'd be starting once the wire option is gone.

Only going by the Xenon schematic, the bumpers are not listed on either the lamp driver or aux. driver board.

Embryon schematic does have them listed clearly on the lamp driver board section. So they definitely are controlled in Embryon.

Pretty sure Xenon's bumpers are part of the GI though and there are only two seperate GI "chains" to the playfield, both coming through J1 on the rectifier board.
This connector can become burnt so be worth to check it out.