Hi, back in the 70's and the early 80's only one red lamp was used on both wagons and carriages. They were paraffin lamps, so they never changed colour. I'm not sure about the side lamps on the guards van? Because I've never seen them lit in my experience in the railway, and I can't ask anyone anymore because any of the older guards and shunters that I knew, are all gone to the great shunting yard in the sky. I know during the MK3 new carriage building program( 1983 -89/90) that drivers at the time had an issue with the red lights that were on the MK3 carriage skirts ( under the body). They were being mistaken for signal lights seemingly, so they changed them to clear/ white lights.
Paul......