XJ6 towing electrics

[alderley]

I was told by a towing specialist that the aluminium bodied XJ saloons use positive earth which makes it difficult to fit towing electrics.
However, the Jaguar main agent says that the XJ still uses negative earth.
Could I fit a proprietary electrics kit (as on my XJ8) which takes a positive fused battery feed to supply the wires in the towing connector. Supply is switched on for the relevant wire to the trailer, using a sip of electricity from a supply going to a light in the rear light cluster. If the "turn left" bulb illuminates, a sip of electricity going to that bulb is fed to a solid state unit which acts as a relay switching a feed to the equivalent wire for turning left on the trailer. Obviously, I would also need the unit that detects a direction indicator signal to the trailer and then is used to feed a diode or bleeper in the car.
I gather the towbar itself is a pain too!