Trailer socket wiring

[joderest]

Ok, one for you electrickery experts out there.
The LUMP has the old 7 pin socket which i installed about 4 years ago. Wife just bought a new horse trailer which has the 13 pin socket.
We got an adapter, 13 pin to 7 pin which works fine, but it has dropped out of the socket twice now. As its an extension, the lid of the socket does not hold it in like if it was just the plug.
The old 7 pin socket is "well worn" and i bit corroded now, so thought i would just change it for a newer 13 pin socket.
Wiring diagrams look like the colours are all the same, only addition is for reversing lights, which we can do without (only reverses on fields or at the yard, not on the road)
We do not need the 12 volt supply (no fridge !!!!)
Is it just a straight swap out ?
It looks to be but thought i better ask.

 

[Tony Dyson]

Just work with the numbers and ignore the colours, 1-7 are the same allocations for both 7 and 13 pin sockets.

 

[Jim2]

Ok, one for you electrickery experts out there.
The LUMP has the old 7 pin socket which i installed about 4 years ago. Wife just bought a new horse trailer which has the 13 pin socket.
We got an adapter, 13 pin to 7 pin which works fine, but it has dropped out of the socket twice now. As its an extension, the lid of the socket does not hold it in like if it was just the plug.
The old 7 pin socket is "well worn" and i bit corroded now, so thought i would just change it for a newer 13 pin socket.
Wiring diagrams look like the colours are all the same, only addition is for reversing lights, which we can do without (only reverses on fields or at the yard, not on the road)
We do not need the 12 volt supply (no fridge !!!!)
Is it just a straight swap out ?
It looks to be but thought i better ask.

Has the "Lump" a dedicated MB wiring harness installed, or does it use a bypass relay kit?

 

[joderest]

opps, forgot that bit, 7 way bypass relay.

 

[Jim2]

opps, forgot that bit, 7 way bypass relay.

And which MB is it? Year etc?

 

[joderest]

clue is in my posts !!!!!
ML270 2003 (hence why called the "LUMP")
However, not being rude, but as fitted with a 7 way by pass relay, could be any car, its not connected to the Mercedes wiring as such, just uses a signal.

 

[Jim2]

clue is in my posts !!!!!
ML270 2003 (hence why called the "LUMP")
However, not being rude, but as fitted with a 7 way by pass relay, could be any car, its not connected to the Mercedes wiring as such, just uses a signal.

Yes theroetically every car, and I understand how they work, BUT if you have any car which uses a single feed to the brake and tail lights , then it will not work ( at least it does not work in my 2014 Eclass w212 OM 651) Yet it did work fine in my earlier MB, a 2010 E class w212, which had seperate feed wires for the brake and tail light. I even bought a newer "SMART" relay, which is supposed to identify the different currents used between brake and tail, and "direct" them to their correct function. But no luck. My SIL, who is an IT techie, believes that as a universal smart relay, it may well work in other makes, or indeed in other MB models, but it is not working in mine. And thats why I was interested in your one. But I guess that as an 2003 car, it has the "old" wiring desigh. One function, one feed wire. And for this set up, you don't even need the "Smart" relay. Good luck with adapting your 7 pin to the 13 pin, its pretty straight forward, and I believe that you will not have any problems with that,

 

[M80]

Yes theroetically every car, and I understand how they work, BUT if you have any car which uses a single feed to the brake and tail lights , then it will not work ( at least it does not work in my 2014 Eclass w212 OM 651) Yet it did work fine in my earlier MB, a 2010 E class w212, which had seperate feed wires for the brake and tail light. I even bought a newer "SMART" relay, which is supposed to identify the different currents used between brake and tail, and "direct" them to their correct function. But no luck. My SIL, who is an IT techie, believes that as a universal smart relay, it may well work in other makes, or indeed in other MB models, but it is not working in mine. And thats why I was interested in your one. But I guess that as an 2003 car, it has the "old" wiring desigh. One function, one feed wire. And for this set up, you don't even need the "Smart" relay. Good luck with adapting your 7 pin to the 13 pin, its pretty straight forward, and I believe that you will not have any problems with that,

Would it work if you picked up the relay brake light feed from the rear LED,
and the rear lights feed from the number plate light?
Of course the left / right rear lights would need jumpering at the relay.

 

[Jim2]

Would it work if you picked up the relay brake light feed from the rear LED,
and the rear lights feed from the number plate light?
Of course the left / right rear lights would need jumpering at the relay.

Yes,for the park lights . would be fine, but I will have to take the brake light feed from the 3rd brake light in the rear screen. And for the moment, I don't want to remove the rear seats and parcel shelf etc. It's quite a lot of ripping out. Of course if have to do it, I will but I'm trying to get an MB electrical diagram of the rear harness which will show me exactly which cables feed which function. That's the ideal.Thanks for your helpful suggestions ,appreciate it.

 

[joderest]

Jim 2.
I feel your pain, I really do not like modern cars and their inability to let a decent home mechanic work on them.
Rant over.
The ML has trailer socket wiring which ends in the left hand side rear .just below fuel filler. You are supposed to buy the correct Mercedes trailer socket wiring and it comes with a plug to pick up the vehicle wiring, it was nearly half the price of the tow bar kit, far cheaper to use the 7 way relay. I used the vehicle trailer socket wiring for the signals, just used a meter to identify which wire did what.

 

[Jim2]

Agreed 100%.PJ Jones towbar fitters and suppliers, have a dedicated plug and play harness, and it will give you the basic lighting you need to drive, but if you want to integrate it fully into the vehicle canbus, it has to be coded by MB. But my local dealer refused point blank to do it...."we do not have any thing to do with towbars " I think that by his way of thinking, anyone who puts a towbar on a Mercedes Benz, should not be allowed to own one