The lamp on the front right (or left, if looking at the front) connects to a metal power switch underneath. When it is pulled out it is off, when slid in it is on. All the old power C12s turn on and off this way to make the sliding switch, which usually sticks straight out the front on old power trains, work with the front coupler that is attached. The C12 was originally designed to push a rotary snowplow in the early 70s but old power C12s that continued to be produced into the early-mid 1990s all worked this way.
I have a page about the Hong Kong C12s also manufactured for Stelco on my website here
