Wiring in a Soviet change house

Hello! Tell me, please, where can I find circuits for electrifying change houses (construction trailers, kungs) of the Soviet era? Here's the thing. In the old cabins (the car looks like in the pictures from the Internet, I attached the second one, there is electrical wiring. There are places for 6 or 5 lamps, two switches (3 lamps on the ceiling in the cabin, one in the vestibule, there is also an open metal "cup" with four two-wire wires with stripped ends, pairwise connected and one long loop of the same wire without an end or connection (for what?), an opening with a pair of wires above and to the right of the door, switches inside the tambour wall outside and on the tambour wall inside it ). I prot the whole system works from two wires (by a wire we mean a single-core half cut along a flat aluminum two-wire cable) coming out of a round hole together with a bundle of other similar wires near the shield (= behind the shield), connecting three lamps on the ceiling parallel from lamp to lamp, but in the hole in the wall near the shield, where the ends of the working wires are led out, there is a large bundle of 15 single-wire wires, 6 of which are paired (thick two-wire aluminum black and gray PVC (?) insulation, cut along only at the exit) and 3 are clearly cut from the same paired (two-core), but so that nowhere without breaking the wall can they find a pair. The question is why the remaining 13 wires (= halves) were used if two (= one double) currents go to all points in the cabin, including two switches and a place for a cartridge in the "vestibule"? If the previous owners changed something, then what is the initial (factory) scheme for electrifying the trailer? After all, they were manufactured industrially and they have some kind of general electrification scheme.