mk1collector wrote:

Led lights only work one way so swap the live and earth over and try again

Alien wrote:

Have you tried plugging the old lights in to eliminate faulty upgraded LED's?
If your getting brake lights at your tow plug I'd be suggesting the LED's are wired wrong.
It was hard to pick up if the MOT was done after the LED upgrade was fitted or prior.

First thing I did Yeah.

This is where I'd be starting...
.Swap the old lights in and test.

Tested, no light except for the rear running light, bulbs OK.

If no brake lights with a test light or multi meter check...
-power feed to the brake light switch (I'm thinking blown fuse here)

Yup, checked and tested, both bulb and live feed (with ignition on)

-power from the brake light switch
(I see you joined these wires for testing but was there power supplied with the ignition on?)

Yeah, even took out the plug to ensure it works. Decided that a much better way would have been to just use the multimeter, with the plug in-house

If you're happy power is being supplied test...
-power at the brake light plugs with the LED's disconnected, check all 3(2 side + high mount).

No power on both, haven´t checked the high mount yet

-check there is a good earth supply at the same plugs.

Have not checked this, as I assume good earh due to running lights OK (same connector)

If all this tests OK the problem is in the LED units.

As the old lights did not work either, I am at loss

I recently had an issue with an upgraded LED upgrade on a lorry at work.
It was a combined park/running indicator unit.
With runnining lights on we had no indicators but OK with them off.
Turns out they had the indicator earthing via the running light circuit
A quick swap of some plugs and it's all good.
I suspect you have a blown fuse or a similar wiring issue wit the LED's.

Thank you very much for your reply:
I have tried pretty much everything you suggest. Ref my answer in between your reply.

I am going to check again tomorrow if the earth-point behind the rear wheel is good. I could not find it today when checking. But as I have been intensely studying the wiring diagrams, I find no other logical explanations to the weird "brake light to rear wiper" signal.. I used a circuit tracer, and ended up with a signal on the green wire that goes into the rear wiper.. Though no other issues.

All lights on trailer works, indicators, running light and side marking lights... But no brake light...

Alien wrote:

If no high mount either double check the fuses.

AND welcome to Defender2.net

Thank you Been a lurker with a series-name.. But with my "extreme" build, I hope to be more active.
Yeah, quadruple checked (just wish I learned NOT to mount the fuse-cover each time Even checked all fuses with a multimeter to make sure. I am thinking I might be diagnosed with OCD on these darn brake thingies!