Had a mail from DLS asking me to return the relay, which I will do.
In the meantime, I found a lampholder and a 21Watt flasher bulb and decided to connect it to the r.h. flasher connection on the 12N pick up connector located in the loadspace and the ground header terminal nearby. My idea was to duplicate the effect of having an additional load-such as the trailer/caravan hitched up. Switched the r.h. indicator on and the dash warning lights went out, the flashers and hazards were not working. The indicator fuse (15A) in the passenger fusebox had blown together with the 15A hazards fuse in the engine bay fusebox

Checked my "Hookup connections and they were sound, not shorting out. Removed the hookup lamp, replaced the fuses and I still have the same symptoms with the trailer warning lamp. Refitted the original relay, hooked up the lamp again and it flashed merrily away, albeit at a slightly faster rate than with it disconnected.
I am convinced that the replacement relay is duff.
The towbar wiring is foolproof and straightforward. The 12N connections as you know are sitting there waiting and ready to be wired in, either by a custom connector on the 12N socket/lead assembly from Land Rover or by direct connection to the individual wires using crimp connectors or soldered & heat shrunk joints..NOT the Scotchlock connectors usually supplied-they are crap and cause untold problems. Replacing the relay is not rocket science..just remove the original and replace it with the 4 pin new unit, the pin configuration ensures that it will only fit in one way. The 12S (Auxillary power) socket is a bit more involved but I will leave that for another day in order to stay on topic.