Wiring up towbar. Colorcoding? (EU version)

I'm trying to wire up my towbar.

I measured some voltages at both rear-light plugs.

I cut open the wiringloom near the fuel fillercap and am cutting the wiring, soldering in an extra lead and heatshrinking it all back together. This all goes to a 10-wire insulated connector that I can leave dangling until I actually fit the electrical connector next to the hitch. This is the reason for trying to splice off all wires in the same spot.

But I am running into some issues.

For one, the plugs that go into the rear lights seem to have a red ground wire and a black&white one. The black&white one near the fillercap (two thin ones, it also has a bigger and a very big one) don't seem to attach to the plugs. I am assuming the ones in the lightplugs go back to the trunk, but as I have all my soldering gear in the trunk, I haven't looked under the floorcover yet. The ones running alongside the fuel-filler-cap cause my diodetester to go berserk.Which is strange unless black&white isn't actually ground... (When measuring between the cut wire and the plug of the lights, which should be measuring between two grounded wires according to my assumption, it shows 2V and a horrific sounding screech instead of the open circuit 3.2V (and no sound) or the 0.000V with the normal beep: it isn't supposed to be able to produce screeching sounds... )...

It does interfere with my assumption that a fat wiringloom comes from the front to the fillercap and starts splitting off there (left rear light), go alongside the bumper and resurface at the right rear light. There only a few wires go on from there.

Does anyone have an official wiring loom color coding chart?

My preliminary findings:
Left light:
Brown with gold dots: rear light
Yellow: indicator
Blue: brakelight
Green: foglight
Red: ground
Black&white: ground

Right light:
Brown with gold dots: rear light
Green: indicator
Blue: brakelight
Green (yes, second green wire in the plug...): foglight
Red: ground
Black&white: ground

Will try to post pics later.

 

I completely forgot the reverse signal

Logical, as I let my kids control the brakes and the lights. Having them Having them put it in reverse while I stand behind the car is something better avoided...

But the red wiring is the reversing lights.

And the small black-whites, together with the biggest black-white is grounded in the middle of the boot under the tray.

One more strange issue: one of the brown cables which I thought was the normal rear-light, turned out to control a relay next to the battery. By the sound of it the black module next to it (edit: something to do with the brakes). I reinstated that wire to its original state (without an extra splice) and found the correct brown cable.

So here's the colors I found. Do note that there are 3 or 4 red and 4 or 5 brown wires in the loom next to the fillercap. So it's hit and miss if you splice them off there...

Left light:
Brown with gold dots: normal rear light
Yellow: indicator light
Blue: brakelight
Green: foglight
Red: reversing light
Black&white: ground

Right light:
Brown with gold dots: normal rear light
Green: indicator light
Blue: brakelight
Green (yes, second green wire in the plug...): foglight
Red: reversing light
Black&white: ground

 

I read somewhere that you can simply hook up the lights in parallel (trailerlight parallel to rear-light). So far I only tested with my DIY "are_all_the_trailerlights_hooked_up_correctly"-box which draws next to nothing and won't change the frequency. (bunch of LED's in the form of left and right light cluster on a 5m extension cord so I can check correct wiring of trailerplugs while sitting in the drivers seat).

I was going to test with real light clusters for the bicycle rack tomorrow

I already made up a relay-box like the one you made, but figured I'd try without first.

My father in law just bought a trailerhitch for an Espace for 107euro delivered last week. It came with an electric box which does what the relay box does. I wrote the seller how much such a box would be, can't be more than 20 euro or so given the whole hitch (10+kg of steel) + plugs + electronics is 87euro....

I did extensive research on finding such a box before I threw the same 20 euro's in parts into a DIY version, but never came across one...

It has two VNQ5050 chips in it... (couldn't resist opening the box up)

 

Frequency is the same with or without bicycle-rack light cluster. Didn't know about the mandatory indication of bulb failure. If the frequency HADN'T been the same, that would have been an indication by itself

I'm considering using my relaybox OUTSIDE the car if ever really needed. Yours must always be working (and making noise) right?

I did a full 13 pole Jaeger plug, so I will also have a switched and continuous live wired in (haven't found a switched live to drive a relay yet, but all cables are wired in the plug and end near the battery). That way I can plug in my relaybox outside of the car, including the 12V to feed all lights from a separate 20A fuse, when needed.
BTW: my relaybox has 6 relays, not just for the indicators... Overkill??? Maybe...

And as for your diode solution: nice! I at first wanted an active electronic solution instead of relays, but decided against it due to the voltagedrop. Later I thought that it indeed does put out a steady 14V so I probably shouldn't be worried about loosing a volt or two.
But you used 5A diodes or even more? The standard 1n400x wouldn't cut it.

I used a similar configuration nearly 20 years ago to switch on a 230V~ load (a 1980's TV) when remotely switching on my laserdisc player... Small resistor in the 230V~line that dropped less than 1.5V when in standby, but more than 1.5V when ON: this voltagedrop switched an optocoupler-LED, and thus a relay with the transistorside of the optocoupler. Parallelled three series diodes so the voltagedrop would never be more than 1.8V over the optocoupler LED(which still had an extra limiting resistor) and a single diode in antiparallel.
The thing is in a cupboard now, but last I checked, it still worked (Triacs can probably do a better job, but I don't understand those well enough)