In the IBM installation they had a relay in the first troffer of each string. They did try to be consistent that it was in one particular corner of each room so you were not looking all over for it. Later they put an adhesive "dot" on the lens frame of the troffer with the relay. That made it real easy to find. This was all 277v so you got a bunch of lights on a relay.
Usually finding the bad switch was just tactile. You looked for the one that was binding on the cover. Until they came out with the small rocker switch, there were a few different approaches. One was making the rocker smaller with a file, the other was making the hole in the cover bigger. Most important was being sure the cover to switch alignment was right. If you had a bunch of switches under one cover, you had to be sure each switch was aligned perfectly, relative to the rest, so the cover would "center" over all of them. That wasn't a big deal if there were only 1 or 2 switches but in the big computer rooms you have a bunch of switches in a row.
