As Chris states the rear set of batteries (if fitted) feed the RJB (Radio Junction Box) which is to the left of the commanders cupola, there will still be power to the RJB even with no batteries but the engine has to be running..
From the RJB 2 core power cables are run individually to the radio sets , and either an IB2 or IB3. The 2 core cable is terminated in a 2 pin female connector at each radio set and IB3/2
From the IB2 or IB3 a 12 core cable ring is run around the vehicle feeding into and out of the different Clansman boxes returning to the IB3 or 2.
As stated elsewhere no Clansman radio set is needed, nor needs to be fitted.to operate the intercom, The yellow fronted (ANR) boxes are the best option, but then the correct ANR headset needs to be used with the ANR system.
There are some weird interactions between between the rear batteries and the vehicle if the rear batteries are not kept charged, If I remember correctly this is referred to elsewhere on the site, I've also noticed it too.
Diana