Thanks ZH875 and
The Oberon
I guess that it looked like https://www.ebay.co.uk/itm/TACAN-Typ...59e2%7Ciid%3A1 It may not have had the Cannon type connector on the front. Strangely, that eBay item refers to a Lightning, yet on a visit to RAF Binbrook myself and my line manager asked where the TACAN coupling unit was situated and it was NOT of that type, but the diecast unit.
https://www.google.com/search?q=taca...-_93kOMKc5lcM:
There were a few types of each, the diecast one either having two identical round multi-pin sockets or one small one large. The one I have just purchase marked Belfast had a two-gang linear potentiometer to drive two range indicators - two large sockets, the other version just a single gang for one range indicator. The large box type had syncros to drive the range display. But saying that, there was a version with a single gang potentiometer for the range indicator. ( By two gange and single gang, I am referring to a means of driving the external displays. There was also another potentiometer within as part of the analogue calculation of range.)
What always puzzled me was that in Air-to-Air Mode, the pilot would see from the Range Indicator how far the tanker was away, but no Bearing information. Sounds like fun in a Lightning with not a lot of endurance...
Clive