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Tow bar installation (live feed)

  • 11-09-2021 9:35am
    Registered Users Posts: 364 ✭✭ mufflets2

    Hi all

    and thanks in advance for any help offered

    I am about to put a towbar with electrics (7pin) on my 2012 1.5diesel quashquai

    I will be using a TEB7AS relay which requires a constant live feed

    Has anyone done this themselves?

    The relay requires a constant live

    Am I correct in assuming that only way

    to do this is to run a new cable from the battery through the firewall inside the car somewhere

    and back to the relay

    any advice




  • Registered Users Posts: 1,701 ✭✭✭ newmember2

    No, you would be incorrect in your assumption, how do you imagine your rear lights are powered?

    I would seek out someone with more vehicle electrical experience for the electrical side of this towbar install if I were you.

  • Registered Users Posts: 339 ✭✭ Dirty Nails

    That's the proper thing to do unless you're able to properly connect to a feed wire to the fuse box. Make sure you fuse that wire - it'll be the only fuse for all your trailer lights.

  • Registered Users Posts: 364 ✭✭ mufflets2

    Rear lights are not powered by a constant live (which a modern TEB7AS towbar relay requires)??

    Thanks for the comments lads but this being a "DIY car maintenance forum"

    ill wait to see if i hear from someone who has already done one.

  • Registered Users Posts: 339 ✭✭ Dirty Nails

    "ill wait to see if i hear from someone who has already done one."

    You could read post #3 or follow the instructions that came with the relay.

  • Registered Users Posts: 7,522 ✭✭✭ PsychoPete

    Whenever we'd fit tow bars it was always a live wire to the battery with an in-line fuse

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  • Registered Users Posts: 339 ✭✭ Dirty Nails

    Exactly. Or to a fuse box main feed if it's difficult to get through the bulkhead.

  • Registered Users Posts: 7,522 ✭✭✭ PsychoPete

    Thats how we done it in a Renault main dealer anyway. Used to get a company in to fit tow bars and they'd just wrap the wire around a fuse, shove it back into the fuse box. They were pretty rough

  • Registered Users Posts: 364 ✭✭ mufflets2

    Thanks for that

    Did ye run the wire through the firewall and then through the car roof pannels??

  • Registered Users Posts: 364 ✭✭ mufflets2

  • Registered Users Posts: 364 ✭✭ mufflets2

    Thats what I thought , Is the best route through the bulkhead up the pillar and back along the roof?


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  • Registered Users Posts: 7,522 ✭✭✭ PsychoPete

    Whatever way is easiest. You could tuck it under the headliner, under carpet or even underneath the car if you wanted

  • Registered Users Posts: 339 ✭✭ Dirty Nails

    Are you ok Princess? You got professional advice (free) in post 3, but you were too busy being butt hurt by the wannabe in post 2 to actually read it :)

    Make sure you use a feed wire capable of carrying potentially 100w & use a 20A fuse.

  • Registered Users Posts: 364 ✭✭ mufflets2

    My appologies I got you mixed up With "newmember" as you said.

    you were correct and i am grateful .

    Im pretty sure I got the right wire and its in now.

    Ill hook the thing up tomorrow .


  • Registered Users Posts: 200 ✭✭ MAYOMICK

    Could you connect up to boot light or is there a power socket in boot

  • Registered Users Posts: 1,701 ✭✭✭ newmember2

    FFS...the comments in this and others are talking about routing a cable through bulkheads and whatever the you not think you might find a constant live in the interior cabin part of the I'm out.

  • Registered Users Posts: 5,394 ✭✭✭ jmreire

    If its a Mercedes Benz w212, it will have an auxiliary battery in the boot, so that solves the power supply in that case. For any other make, I'd connect a fused ( 20 A MAX ) cable direct to and as close as possible to the battery ( unless of course, you have a wiring diagram for your particular vehicle, and can select a "free" fuse connection from the fuse box, this will eliminate any routing of cables from the engine compartment). But no way would I take a feed from any of the interior electrics. Personally, I've never had any problems running a cable from the battery, one drilled hole ( and sometimes, its possible to feed a cable through the bulkhead via an existing cable feed.) routing it back under the carpeting along the inner sill panel, is no big deal either. Thats your live feed organised. If you are using a "Smart" relay, ( versus a Factory approved plug and play unit ) and using it by connecting the "trigger" wires to each of the light functions, IE-Brake, Park, L+R turn, and / or Foglamp etc. Bear in mind that most modern car electrics are LED, and the park/ brake light uses the same cable..additional power is sent to the same bulb ( LED), causing it to glow brighter, giving the brake light effect. All the other functions are the same as any normal set function , one cable. The so called "Smart" relay, is supposed to differentiate between the brake and park function, sending the appropriate current at the appropriate time. Now,in my case with the MB w212. despite trying several Smart Reays...I cannot get the brake function to if anyone out there has wired a MB ( has to be a w212 from 2013 onwards....earlier models did not have the LED rear lights , and the smart relay worked fine in these models) Maybe, your 2012 car will have the old type electrics ( 1 cable for each function , and not LED). in which case, your smart relay should work fine, Good Luck with it/

    So any questions, fele free to ask, and please let us know how you get on, OK?

  • Registered Users Posts: 4,071 ✭✭✭ johndaman66

    I'm currently fitting a towbar to a 2011 Avensis. Towbar itself on. Not without a struggle as none of the 3 bolts holding on the base plate on one side wanted to go in fully (likely from 10 year of dirt/ silt from the road having accumulated up there and hardening). Got past that by cutting down about 10-15 mm into the centre of the threads in a slave bolt, driving it up all 3 holes and all 3 bolts went in easy then.

    About 90% of the wiring done - certainly the "heavy lifting" part I was dreading. Just need to run the towbar socket wire into the can bus module. All I'm short is a ring connector to earth it to the chassis which I overlooked and will pop into town tomorrow to pick up. Re the permanent live feed I ran it from an existing permanent live circuit not in use in the fuse box under the glovebox. It is the panoramic roof shade - "wagon only" as per owners manual. Either way my car certainly does not have a panoramic roof shade. I effectively "piggybacked" of this fuse and ran the wire back along the sill of the car and into the boot all along the existing wiring harness. I used a product the same as below;

    Guessing going by the book the permanent live should be run back directly from the battery. In my case the only place I could see that I could access to run the permanent live wire through the firewall was where the existing wiring loom entered the cabin from engine bay. I say access but in reality access is very limited from both sides. My heart sunk slightly anytime I looked at it contemplating trying to somehow put a hole in it and likely damage the existing wiring😭 Wouldn't really want to go there.

    I'd probably advise against running the wire back along the headlining if possible. If you start pulling at that it could end up being problematic and not go back up right. Think too once that gives a bit over time it'll give way more and more. In my own case I needed to remove the plastic sill covers on the front and rear doors. a small kick panel down in front passenger footwell and the lower seatbelt cover in the B pillar. All are plastic and popped off and on easily in my case. Had to lift the rear seat base also which came up easily also. Really and truly I was following the existing wiring loom for the whole run - adding a few layers of insulating tape around the new wire and existing loom. Apart from not hooking up directly to the battery I a following the below to a T which is actually the same as the relay module I am using;

    Guessing that piggybacking of an existing, albeit unused fuse like I am doing is not recommended by the book practice but as an amateur chancer I'm going to take a punt on it. I take some solace in the fact that I'm likely doing a neater job than the so called I'm assuming "professionals" mentioned as per post #8. Would be nice to have the battery in the boot though as per post #17 - would make the job infinitely easier.

    Post edited by johndaman66 on

  • Registered Users Posts: 5,394 ✭✭✭ jmreire

    So have you gone for the dedicated canbus system, complete with dealership coding? Or did you go for the by-pass relay? In my personal experience, I've always gone for the floor routing of the live feed, and i've never had any problems with it in any towbars that I've ever fitted of using the bypass system, and I've fitted a fair few, from time to time ( present project is fitting one to a 2014 MB E220 W212, and it seems that it does not like the by pass relay if any one out there has experience ,, and fitting a bypass relay, you might give a few tips. On an older MB E class, 2010, the relay works fine....but the 2014 MB has the can bus system not recognizing the smart relay.

  • Registered Users Posts: 4,071 ✭✭✭ johndaman66

    Apologies jmreire, the second link in my post was the incorrect one (I had a few different tabs open on the subject in hand and inadvertently linked the incorrect tab). Apologies if it caused any confusion and I have updated my original post accordingly. To confirm I am using the by-pass relay.

  • Posts: 0 [Deleted User]

    I read the Nissan Qashqai GENUINE ACCESSORIES brochure and there was the next information.

    "Kit includes Towbar Wiring Harness."

    If you buy the genuine towbar kit, you get the wiring harness too. So, why all that story? Aftermarket parts? Is it really worth that?

    EDIT: After bit digging the information I suggest to go genuine because DAS can go mad.

    Post edited by [Deleted User] on

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  • Registered Users Posts: 5,394 ✭✭✭ jmreire

    Part 1.....The problem I have with my 2014 E class is that the Brake / Park light are fed from a single cable. When you press the brake, additional current ( if thats what you call the CanBus setup) is sent to the LED causing it to glow brighter. So one feed, 2 functions. Now, I've used the standard bypass relay for many tow bars in different makes of cars,, never a problem. Now fast forward to cars using CanBus, and even with the newer "Smart" bypass, which is supposed to differentiate between the pulses, Brake and Park, and send the correct voltage to the correct trailer light, All very fine, except it does not work in my 2014 E class.

    Part 2,,,,,, I can get an approved "plug and play" setup, and it will give me what I need to be " street legal", Stop and tail, L+R indicators, Fog lights etc. But if I want to hook it up so that it covers all of the functions ( Trailer recognition etc) it will have to be coded to the car by a main dealership. And this can be a costly business, price of MB wiring harness ( Plug and Play ) + Coding costs, ( and as far as I know, it has to be coded by the dealership. But someone out there may have more info on the subject.

    Part 3...... Individually take the by pass relay cables from the rear window brake light for the brake feed, and the Taillight feed from the Nr plate lights. Has anyone successfully managed to connect a bypass relay to a MB from 2013 onwards?

  • Posts: 0 [Deleted User]

    The Nissan information:

    TRAILER DETECTION (where fitted)

    When towing a trailer and the turn signal switch is

    used, the electrical system of the vehicle will detect

    an additional electrical load of the trailer lighting. As

    a result, the trailer direction indicator light comes on.

    Sure it need the coding, nothing is plug and play.

  • Registered Users Posts: 5,394 ✭✭✭ jmreire

    Sure that's normal in either the bypass or "Plug and Play" set my particular case, its the Stop /Tail lights I have the problem with. The "Smart" relay does not recognize the different pulses sent to the Brake light,, and so only gives ( in my case, tail lights) In my previous MB, 2010 E class, each electrical function has its own "Trigger" cable, so no problem. I'm just wondering if its only MB cars since 2013 , or does it affect other makes too? For the Nissan and Quashai cars which are under discussion. how has it worked out for them? And as for the Plug and Play set up, for sure I've seen it work without coding, gives all you need to comply with the legal requirements, but its not integrated in the CanBus system.