1971 Questions for all other cars electric guages

Electrical problem
1971 Questions for all other cars V8 Two Wheel Drive Automatic 500K miles

coming home from weekend trip all guages quit, fuel, voltage from alternator, water temp, oil pressure. Have back up mechanical guages in rear of bus, bus is 1971 flxible, old LA city transit converted to motor home. 12v buss bar from house batteries is supply for instruments as normal bus wiring is 24v. Old indicators were idiot lights. Suspect I lost voltage or ground to guages. Is this correct wiring: sender to one term on guage, other term to common 12v supply. Case is ground. Dash lights also out. I started conversion in '93 so do not remember how guages are wired and did not draw schematic as I installed them from mfg spec sheets. Believe I used 12v to off/on switch for supply with all guages fed off of one wire looped to all guages. Used case as ground as guages were mounted in a metal plate. Senders went to other terminal on guage. Guages are generic from local auto parts store, no name on them. I used manual off/on switch with fuse to completely shut down electrics when bus is being stored for long term. Bus has manual shut down for 24v disconnect.