James , all Pz III 141's from E series to N were essentially the same interior wise . The alphabetical designations were from changes in armor , armament , power plant etc.
Your Pz III M got its alphabetical letter for the raised exhaust for wading and brackets for side armor , otherwise it's an L , which became an L because of the larger gun , ..... etc. on down to the E which was the first mass produced Pz III .
If you look at the cutaway pic , upper left you can see an electrical junction box on the side wall .
In the real 1/1 pic you can see the same el box . What's really cool and this is just spitballin but above the gauges next to the vision port is another el box which I believe is the on/off switch for the lights .
You're never going to find pics of the wiring where it comes through the front hull plate below each light into the tank . It appears that the wires are not in conduit from under the lights to the first junction boxes , then it looks like conduit from the boxes to the back of the tank .
Hope this helps and I was able to explain this sanely .