My D-max has the Euro 13 pin towing socket already fitted, from my own testing, pin no.9 (leisure battery charging) is constantly live all the time, now if I plugged in a caravan/camper unit isn't there a possibility of draining the trucks battery whilst stationary overnight etc? I've tested pin no.10 (fridge charging) and that is only live when the engine is running, now that makes sense to me,...I just wonder why Isuzu didn't wire pin no.9 to operate in the same way.

OK, so I have since bought a voltage sensing relay, I gather that is the best thing to fit anyhow, how have you guys wired them into the towing loom? Now do I run just one wire along the whole length of the truck, to where the towing connector is actually situated and cut/wire it to pin no.9 or is there a more suitable place to splice into closer to the engine bay for example??
Here's links to the connector and relay I have.

https://caravanchronicles.files.wordpre ... ket-01.jpg
https://www.tridenttowing.co.uk/images/ ... 8_zoom.jpg