Towbar wiring for a W212 E350 estate 2011

[JcbPaul]

I used the Aux Battery in the boot as a power supply on my E250 and it works fine. I also located the unit in the space next to the battery

The kit i had included a fuseable lead so all is good.

The kit i used also senses whether the tail / Brake lights are activated from a single cable so the wiring was pretty simple

Thanks for your reply it sounds like the kit i have. I will be having a look at it today.

 

[JcbPaul]

Hi, No. I wouldn't advise it. If your nearest power supply is the cigar lighter on the console between the front seats, it's that or from the battery direct. Bear in mind that those cigar lighter sockets can be fused for pretty high amperage, so better use a smaller fused link on the cable, as near the socket as possible.
Its not such a big deal running a cable direct from the battery to the boot either, especially if you have access to a lift. Same conditions apply... fusible link, as close as possible to the terminal. I've done it several times, and is a bit awkward, but not too much either. Best of Luck with it, and you are lucky in that in the 2012 E class, the brake and park lights are standard bulbs, needing a separate feed, unlike the 2014 E class,,they have the new system, one micro cable supplying both brake and park lights

I was just checking the tail lights and they are all LED bulbs except the reversing light is a standard bulb. So would i be better off to wire it from the centre brake light as you did? Thanks.

 

[Justintyme]

I was just checking the tail lights and they are all LED bulbs except the reversing light is a standard bulb. So would i be better off to wire it from the centre brake light as you did? Thanks.

Yes, if it just has the single feed to both the park and brake light, then you will have to take you brake light feed from the 3rs brake light. The so called "Smart " relay are supposed to differentiate between the brake and park feeds, but I couldn't get it to work in the ones I tried.

 

[Justintyme]

I used the Aux Battery in the boot as a power supply on my E250 and it works fine. I also located the unit in the space next to the battery

The kit i had included a fuseable lead so all is good.

The kit i used also senses whether the tail / Brake lights are activated from a single cable so the wiring was pretty simple

 

[Justintyme]

I used the spare battery in one of my cars as the supply, and it worked out fine too. Then I was transferring the hitch to another MB that I had bought, so I removed it from the 2014 one. As I was unhooking the hitch power supply from the small battery, I accidently disconnected the main cable (mistake) from it and when it was re-connected, the dash lit up like a Christmas tree. I cleared most of the codes, but the battery in the boot code stayed on. I was trading it in next day, and told the salesman about it, but he thought it was just needing a new battery. I'm not sure if that was what was wrong. Anyway, if I am using the small boot battery ever again, I'll make sure that the main lead from the small battery is not disconnected, not even for a second.

 

[ALFAitalia]

....and you are lucky in that in the 2012 E class, the brake and park lights are standard bulbs, needing a separate feed, unlike the 2014 E class,,they have the new system, one micro cable supplying both brake and park lights

I thought they were all LED by then.....my 2010 W212 saloon is.


EDIT....did not read far enough!!

 

[JcbPaul]

Yes, if it just has the single feed to both the park and brake light, then you will have to take you brake light feed from the 3rs brake light. The so called "Smart " relay are supposed to differentiate between the brake and park feeds, but I couldn't get it to work in the ones I tried.

Thanks, i took the live feed from the 12v socket at the centre console and fitted 20amp fuse hidden underneath the air vents. I took brake light from the 3rd brake light. I am just replacing a split intercooler hose on it now!

 

[Justintyme]

No problem! Hope that all goes well for you!

 

[Justintyme]

Thanks, i took the live feed from the 12v socket at the centre console and fitted 20amp fuse hidden underneath the air vents. I took brake light from the 3rd brake light. I am just replacing a split intercooler hose on it now!

Thanks for your reply, glad that it worked out for you.

 

[Chalky600]

I used the spare battery in one of my cars as the supply, and it worked out fine too. Then I was transferring the hitch to another MB that I had bought, so I removed it from the 2014 one. As I was unhooking the hitch power supply from the small battery, I accidently disconnected the main cable (mistake) from it and when it was re-connected, the dash lit up like a Christmas tree. I cleared most of the codes, but the battery in the boot code stayed on. I was trading it in next day, and told the salesman about it, but he thought it was just needing a new battery. I'm not sure if that was what was wrong. Anyway, if I am using the small boot battery ever again, I'll make sure that the main lead from the small battery is not disconnected, not even for a second.

well you will need to dis connect it to replace it, maybe there's a procedure?

 

[Justintyme]

well you will need to dis connect it to replace it, maybe there's a procedure?

Yes, I think that's what happened. When I was fitting the towbar to the 2014 E class, I undid the nut on the battery clamp and immediately put the prepared cable on the battery bolt so no loss of connection between the battery and the car electrics. More, recently, I had to replace the main battery in my 2018 w213 E class, and while the changeover was taking place, the mechanic placed an alternative power source or a by-pass if you like, into the OBD port. So no problem, no warning lights or codes showing. But what I still cannot understand is why a battery which had previously behaved impeccably, failed purely because it was disconnected.....

 

[Justintyme]

Thanks, i took the live feed from the 12v socket at the centre console and fitted 20amp fuse hidden underneath the air vents. I took brake light from the 3rd brake light. I am just replacing a split intercooler hose on it now!

Matter of fact, the cigar lighter, due to the nature of what its designed to do, carries a 20 amp fuse, but I suggest that you replace it with 5 amp one. Would be safer.