How to connect switches to power transformer?
I would put the red switch in the same wire as the fuse - that should be the Live wire.  For AC wiring, you should always switch the "hot"/Live wire, not the Neutral.

I would put the -26V switch in the -26V wire, rather than in the Ground.  Either way would work, but it makes more sense to me to switch the "hot" wire.  The lamp lead for the -26V switch should go to GND, but if it is desigend for 230V, it probably won't light with only 26 volts.