Composite to Scart
These are not quite as simple as they first appear. They send the composite video signal of up to four inputs to the correct pins of a corresponding Scart plug. Additionally they send 12 volts (from the DC input) to the appropriate pin of the Scart plug. This instructs the television to switch to its Scart input and tells it the Scart input is in 4:3 resolution. On some televisions it automatically switches the television 'ON' out of standby mode.
The 12V input is such that the outside should be deemed Ground, and the centre should carry +12V.
The grounds of each of the four composite inputs are not connected together, nor to the 12V ground, as either is pointless and silly (groundloops?).
The pin assignments of the four pins on the four-pin XLR sockets are as follows:
1 = 12V Gnd,
2 = Vid Gnd,
3 = Vid Sig,
4 = +12v
Note: the power is such that the 0V and +12V are the same as for our cameras, so the cameras shouldn't be damaged if somebody foolishly (or perhaps as part of a desperate bodge) plugs the camera into the box - provided the power supply at the DC plug is the correct polarity. However, if the mains to 12V supply used isn't powerful enough the camera will probably quickly turn itself off.
The pin assignments of the four pins on the Scart plugs are as follows (I think):
8 = +12v,
21(outer metal) = 12V Gnd,
17 = Vid Gnd,
20 = Vid Sig