I had one reference from a RC guy in the UK who said the rear ones were red (not that they worked as brake lights) and the cylinder was an intercom jack, so I ran with that.
It looks awesome and works great too! I just am pointing out for anyone who may see this and base their rear light on the kit.
Postwar upgrades used the intercom button in place of the light.
Here, from my walk around sets, we see that it is a call button on this example:
Regards,