No, not at the L322 but at the who had it before me and completely hacked up the rear end!

OH MY GOD WHAT A MESS.

Apart from taking a jigsaw to the plastic under-body for access to the tow hitch as apparently learning how to under 4 small plastic screws was too hard, apart from grinding off the mounting bracket for the 7-pin large round socket on the tow assembly and loosely / dangerously relocating the trailer socket to the now hacked up plastic under-body that is now only has 3 small plastic screws holding it on as well as the weight of the trailer socket, apart from chopping off the LR 7-pin large trailer socket and replacing it with a Supercheap cheap-n-nasty replacement (yes there is actually an automotive store in Australia called Supercheap and they are quite prevalent, though the quality of their goods sometimes is.. debatable), apart from connecting the Supercheap cheap-n-nasty replacement 7-pin large trailer socket to the LR wiring harness with much much smaller gauge wire and scotch locks - but now, NOW after I remove their crappy wiring and trailer socket and replace it with my own crappy Supercheap 7-pin large socket (ok ok but I needed something that I new the quality of, in that at least if it didn't work I could take it back) and connected the Supercheap 7-pin large socket direct to the LR wiring harness with the nice thick gauge wire, NOW I wonder if they even made this extension up and didn't wire it correctly in the first place

*sigh*

So after I got their crappy Supercheap 7-pin large socket moved from the plastic under-body, I took it to my trailer and tested it - only the running lights worked. No indicators, no brake lights. . Ok, at that stage I figured I'd get rid of those scotch locks (because they can cause no end of possible issues) and I would connect a new 7-pin large socket direct to the LR wiring harness.

There wasn't much slack and it took me almost 3 hours to do but I did it (it was fiddly and my fingers aren't exactly delicate, also there wasn't much slack to play with).

Took it back to the trailer and tested it.

Running lights - check
Left indicator - check
Right indicator - check
Looking good!
Brakes - nothing
hmmm
Brakes - nothing
umm.. wriggle the connectors, wriggle the wires
Brakes - nothing

.

Ok, lets get out the multi-meter and check what goes where and if I'm getting current (for reference, Australian wiring is available here https://findthingy.com/trailer-plug-and-socket-pinout/ - look for Large 7 Pin Round (VIC))

ok, stop lamps should be on connector 6. Test it, nothing. Ok, try running lights to make sure multi-meter is ok. Yup, fine. Argh. Ok, pull large 7-pin round socket back off and check wires at back of socket. Yup, all still connected, no lose wires. Check voltages, nothing on brake wire. hmm.. ok, for some reason one of these wires in purple and it goes to a red wire. Well that maybe a LR specialty, nothing unusual with that but maybe the purple is supposed to be blue so I may have got brake-lamps and service brakes mixed up. Nope, nothing on that line either.

hmmmm. ok, need to go deeper *sigh*

Open tailgate, check fuses. All there at least, all easily identified. Sweet! Doesn't appear to be a specific one for brake lights though, so I'd expect if the fuse had blown it would take them all out.. ok, well lets see if we can trace where the trailer wiring goes. Take out cover over spare tire, oh look there's a connector there, can't quite see if it comes from the trailer socket but looks about right, need to take out the spare tire to have a look. Out comes the spare tire and yup that bunch of cables is definitely the one coming from the trailer socket and going to this connector.

Lets pull the connector apart and check the power is getting that far.

After a little fiddling I manage to pull the connector apart without breaking it (almost a first for me!)

Get the multi-meter out and a small rod for pushing down the foot brake and jamming it against the front seat so the brake light stays on. Checking pins, power, no power, power, no power, no power, etc. etc. Jot down notes. Go to front, take small rod out so brake lights go off. Back to tailgate, recheck pins - power, no power, no power, no power.. AH HA! We have a winner! Double check my work - yup, definitely the second small pin that's getting the brake light power... ok, lets look at the connector and see which wire........... and then I find this.

Click image to enlarge

Click image to enlarge

Is there a red wire at the other end on the 7 pin socket ? If so, must be another end somewhere... .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

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Yeah, it's the big purple wire that they've connected to the slot *below* where it's supposed to go