There's a GREAT wiring diagram for the BX23S in the 'electrical' subsection, post #13 !!! best to download and save it. Super crisp and zoomable !!!
Power from the ign switch goes to a 'glow relay' that then powers the glow plugs and the 'glow lamp' fuse. If the lamp is on, there is power to the glow plugs. The glow lamp relay switch is fed from the 50 amp fuse, so 24/7 it HAS power.
Assuming you pulled that fuse ,it might be the 'glow lamp' relay contact are failing.
In the good old dayze, I'l open up the relay, clean/file the contacts and replace. Today ,it's probably easier to just buy a new relay.
A quik look, it appears to be a 12V, 30A ,5 pin relay,.13 a coil...only $20 at dealer, 4 used on the BX23S.
If it is..then it's 'marginal' . If each glow plug takes 10 amps.... 3x 1 =30 so contacts are 'maxed out'.
You may consider 'upgrading' to a 40 amp 'change over' relay, often used in aux lights for cars, trailers, etc.