Hello, have you find the diagram?
No,I didn't (unfortunately,
and if you do manage to find one, please post it, Thanks ) What year and type is your Merc? For my 1st MB, 2010 E class w212 200cdi. It was pretty straight forward, use a tester to locate the live feed to each function in each of the rear lamp clusters, attach trigger wires to the relay, and job done
.. So what you have to do is instead of taking the brake feed from the rear lamp, take it from the 3rd brake light, and take the park feed from the Nr plate light. Thats one alternative way to do it, but it involves quite a lot of dismantling ..removal of the rear seats to get access to the feed, ditto Nr plate lights ( they are a bit simpler to get at) Now if you( or I ) had a wiring diagram....would make it all so much easier. As I needed the trailer urgently, I did not go ( yet) to the removal of the seats etc.I just took the easy way out, and have Indicators and Brake lights only, which means no night driving with the trailer ( but in any case, I would not be doing much traileting at night anyway ) I thought about getting the MB Plug and Play wiring kit, but that has to be coded by MB for it to work, and the local MB dealership flatly refused to do it. So for now, I drive on with Indicator and brake lights only...and like I said, works perfectly in the day time, but now with the lengthening daylight hours, I will be having another look at it. Meanwhile, best of luck with it, and keep us updated on how you get on, OK?Hi.No,I didn't (unfortunately,
Now fast forward to my newer MB...2014 E class 220, pretty much the same set up, except its a newer wiring system..for the L+R, no problem..identify the live feed and take your trigger wire from there.Then we come to the little matter of the Park / Brake lights, and the problems start. For both lights, its a single cable feeding one bulb, which increases the power to the same bulb when you press the brake. Now modern relays, so called "Smart" relays where you feed the single brake / park trigger into the park slot on the relay, and then the Smart relay ( which I used) is then supposed to "identify" the incoming feed, and split it. Did not work for me, even with a brand new relay ( or maybe I was doing something wrong, even though I did it by the book..I don't know...
fuse-box.info
Thanks for sharing, I had a look but I can't find anything about rear lights, there is something about trailer recognition relay, so I imagine it may be something there where you can tap into, but I haven't got the necessary knowledgeIs this link of any use?
Fuse Box Diagram Mercedes-Benz E-Class (W212; 2010-2016)
Fuse box diagram (location and assignment of electrical fuses and relays) for Mercedes-Benz E-Class (E200, E220, E250, E300, E350, E400, E500, E63) (W212; 2010-2016).
ThanksThis UK company might be of help. Hover over the Products and Technical to find more info.
Mercedes E CLASS (W212/S212/C207/A207) 2009 - 2016 Towbar Electrics
Towbar fitting electrics equipment for Mercedes | E CLASS (W212/S212/C207/A207) 2009 - 2016www.rydertowing.co.uk
Sadly a cheap aftermarket one(Umbra Rimorchi) doesn't provide much instructions for the wiring, which is universal anyway.
Hi John, sorry for the delay..this covid world is crazy, isn't it? Any way some more info for you. I took the power supply for the relay from the live feed to the SAM unit. No problem noticed (Its same "smart" relay as you have BTW. ) Then I checked each cable in the L+R tail lamps to confirm which cable was for which function , and used these wire's to "trigger" the appropriate function in the Relay. L+R indicators, no problem...ditto Reversing and Fog Lights. Then we meet the problem of the single cable feeding both brake and rear park lights....I was unable to get it to work ( Smart relay or not) Only the brake lights are working...no rear park lights. So now, next step for me will be to take a trigger cable from the NR plate light to the relay, and I believe that this will solve the rear park light issue. For the brake Light, I plan on taking a trigger wire from the 3rd brake light in the rear window. Obviously, I will disconnect the existing Brake / Park trigger from the "normal" feed. Maybe some one else has already done this, and if so, would be great if they would share their experience in over coming this problem
On my 2010 Eclass w212, I fitted an approved towbar ( McCabes), and the actual fitting was straight forward with full instructions supplied, for the electrics it was pretty straight forward as well..follow the instructions which were supplied with the relay, and off you go, all lights working normally .( This set up does not connect up with the canbus, so the car will not be aware that its towing a trailer. This is not important to me, as first I don't do much towing to begin with, and second, I only tow light loads. None the less, as I live in the country, I do need to have a trailer.)
So I will have to remove the rear seats and parcel shelf and take a feed from the 3rd brakelight in the rear window, and for the park lights, remove the boot lid trim and take the feed from the Nr plate light. Glad to hear that you got it sorted, and Good luck with your cycling. 
Hi,So in your car, you took 4 seperated feeds to the relay? L +R indicators, 1x Brake light and 1 x Park light? And connected them individually to the relay. And it worked out fine. In previous cars I owned, that was always the way I wired for the trailer. But with my present MB ( 2014 w212 Eclass 220) the brake and park lights are fed by a single cable. And therein lies the problem....with the SMART relay, you only connect the single brake / park cable, and the SMART relay is supposed to differentiate between the 2 different currents, and feed them to the correct bulbs. Problem is that it does not work for me.
www.towsure.com
.
Hi,
This is how I connect them from the Smart relay to the car:
1 Green to the R indicator (3 wire from top to bottom)
2 Red to R break (4 wire from top to bottom)
3 Black to to R tail gate(2 wire from top to bottom)
4 Yellow to L indicator(3 wire from BOTTOM to the TOP)
5 Brown to L tail gate (2 wire from BOTTOM to the TOP)
6 White connected together with the White wire from the 7 pin plug which comes to the relay, both connected together and then connected to the car's Earth.
I solder all the wires instead of the clips, I don't like them.
So I think I had 2 wires comming from the relay which I didn't connect ( Blue is Fog and Grey is reverse which I'm ok without)
That was my settings
Regarding yours, it may be a newer model and different electronics, mine is the first generation of the facelift (I think) 2013 e220.
I have 5 wires going to the light plug so I imagine 1 is brake, tail gate, indicator, earth and the remaining one ...no idea.
On models where tail gate and brake is feeded from the same wire you only have to connect the Red wire from the relay to that one, leaving the Black and Brown (from the relay) disconnected and the relay is supposed to know from the current voltage is getting what lights to action and when.
If you the same as me 5 wires to the light conectors L and R, just make sure you identify them right, because it happened to me when I started( had no experience at all prior ).
Whit the multimeter I had the tail gate on , identify the wire,(so at this stage you shouldhave 12v aprox at only one wire) and the when pres brake I had obviously 2 wires with 12v, because I had the tai gate still on, which confused me (until I woke up and realized is normal) and if indicator is on the same time you have 12v on the 3 of them, but if switched on individually you should have 12v on only 1 wire on the same time, and then you know which wire is what.
The way I've done it with the multimeter was, set to voltage, I probe to the battery negative and the other probe with a needle attached to be thinner, I tried the connector wires one by one, WITH the connector plugged (not sure if makes any difference if is disconnected or not).
You may find to many details, but for someone like me It would have been brilliant to find such a detailed info before.
Here you have a useful link which help me as well
Good luck.How to Fit a Multiplex Bypass Relay - Towsure UK
Supplying the UK's caravan and camping enthusiasts with towbars and trailers, caravan and campervan awnings, family tents and camping accessories. Trusted since 1967 Towsure is your go-to store for all your caravanning and campsite equipment, outdoor clothing and leisure, with shops in Sheffield...
Regarding the bike rack, I've paid for it before having the towbar installed, and it was near Manchester and after lock down was over and able to travel, I planned a 10 days trip on Yorkshire, with the idea that the bike rack and electrics will work,I tied my 2 bikes on an old bike rack(very uncomfortable, no access to the car's boot) and head over to Manchester( I'm from Coventry) get there, swap bike racks and lucky when plugged the connector everything worked, or otherwise I would have to travel without lights on the rack for that period
I try to test the light on the plug with the multimeter after finishing everything but sadly I wouldn't get the voltage corresponding to the correct wires, I had some mixed signal to the plug, it was correct from the wires comming out from the relay towards the plug but not on the actual plug pins, and after several fails I gave up and hopped it should be ok, after knowing I done more or less ok.
And on top of that I installed a dash cam , hardwired from the same fuse box, so more wires, more head ache, but that is working fine as well, still playing up with the parking mode as it record continuous but hope I'm getting there
Here you have my story
All the best.
John
Thanks very much , you have been most helpfull, for sure !!! When you mention Tailgate , your car is an estate? Normally, in a saloon, its called the bootlid. But no problem.Hi,
This is how I connect them from the Smart relay to the car:
1 Green to the R indicator (3 wire from top to bottom)
2 Red to R break (4 wire from top to bottom)
3 Black to to R tail gate(2 wire from top to bottom)
4 Yellow to L indicator(3 wire from BOTTOM to the TOP)
5 Brown to L tail gate (2 wire from BOTTOM to the TOP)
6 White connected together with the White wire from the 7 pin plug which comes to the relay, both connected together and then connected to the car's Earth.
I solder all the wires instead of the clips, I don't like them.
So I think I had 2 wires comming from the relay which I didn't connect ( Blue is Fog and Grey is reverse which I'm ok without)
That was my settings
Regarding yours, it may be a newer model and different electronics, mine is the first generation of the facelift (I think) 2013 e220.
I have 5 wires going to the light plug so I imagine 1 is brake, tail gate, indicator, earth and the remaining one ...no idea.
On models where tail gate and brake is feeded from the same wire you only have to connect the Red wire from the relay to that one, leaving the Black and Brown (from the relay) disconnected and the relay is supposed to know from the current voltage is getting what lights to action and when.
If you the same as me 5 wires to the light conectors L and R, just make sure you identify them right, because it happened to me when I started( had no experience at all prior ).
Whit the multimeter I had the tail gate on , identify the wire,(so at this stage you shouldhave 12v aprox at only one wire) and the when pres brake I had obviously 2 wires with 12v, because I had the tai gate still on, which confused me (until I woke up and realized is normal) and if indicator is on the same time you have 12v on the 3 of them, but if switched on individually you should have 12v on only 1 wire on the same time, and then you know which wire is what.
The way I've done it with the multimeter was, set to voltage, I probe to the battery negative and the other probe with a needle attached to be thinner, I tried the connector wires one by one, WITH the connector plugged (not sure if makes any difference if is disconnected or not).
You may find to many details, but for someone like me It would have been brilliant to find such a detailed info before.
Here you have a useful link which help me as well
Good luck.How to Fit a Multiplex Bypass Relay - Towsure UK
Supplying the UK's caravan and camping enthusiasts with towbars and trailers, caravan and campervan awnings, family tents and camping accessories. Trusted since 1967 Towsure is your go-to store for all your caravanning and campsite equipment, outdoor clothing and leisure, with shops in Sheffield...
Regarding the bike rack, I've paid for it before having the towbar installed, and it was near Manchester and after lock down was over and able to travel, I planned a 10 days trip on Yorkshire, with the idea that the bike rack and electrics will work,I tied my 2 bikes on an old bike rack(very uncomfortable, no access to the car's boot) and head over to Manchester( I'm from Coventry) get there, swap bike racks and lucky when plugged the connector everything worked, or otherwise I would have to travel without lights on the rack for that period
I try to test the light on the plug with the multimeter after finishing everything but sadly I wouldn't get the voltage corresponding to the correct wires, I had some mixed signal to the plug, it was correct from the wires comming out from the relay towards the plug but not on the actual plug pins, and after several fails I gave up and hopped it should be ok, after knowing I done more or less ok.
And on top of that I installed a dash cam , hardwired from the same fuse box, so more wires, more head ache, but that is working fine as well, still playing up with the parking mode as it record continuous but hope I'm getting there
Here you have my story
All the best.
John
Hi, sorry for the confusion , yes its a saloon as you had seen in the picture, and you may be right and the method you mentioned may be the right one for you.
