I have a sneaking suspicion we should move this thread into either the Wireless or the Armour forum.
The original A.C. Daimler used a Control Unit No.1 and Junction Distribution No.1 (for the driver intercom), I think. (Though that was for the WS 19 Mk.1.)
The Junction Remote Control _has_ to be fitted to the turret in order to connect to the external cable reel, and it must be within a foot or so of the other control unit, so I suspect they both go on the underside of the turret roof, the JRC plugs in to the operator's droplead (on the bottom box with two switches), and the operator connects to that. That leaves one or two dropleads free for commander and gunner, and the driver can have a Junction Distribution No.1 or No.3 for his intercom down in the hull - fed via the rotary base junction. (How large is the crew anyway?)
Sigh... having just watched all the clips I can find on Youtube, I don't think you can fit the control units to the turret roof because it opens! Nobody seems to bother to cover the radio fit.
Turret sides, maybe? Are there any mounting plates or signs where they were removed?
Chris.