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Trailer lights repair, Ifor Williams etc.


  • Registered Users Posts: 8,239 ✭✭✭ Pussyhands

    Youtube has a load of good things but it's annoying when you can't find a video explaining what you want.

    I'm trying to learn the theory of wiring trailer lights. I think it's a 7 core plug? So the socket goes to the junction box. Does that mean all 7 wires are then put to a terminal in the junction box? And then each terminal has a single wire going to the appropriate light?

    Then each light has a ground wire from the "return/neutral" side of the light which is all connected back to the ground terminal? Would you be running 7 core cable for all wires even though only the one colour wire would be used? Does the ground terminal then have to be welded onto a metal part of the trailer?

    I'd love if there was places you could learn this type of DIY stuff.

  • Registered Users Posts: 853 ✭✭✭ minerleague

    Sorry you lost calf like that, 7 core wire from car to junction box on trailer, line of connectors in junction box for each of the 7 incoming wires, 2 wire cable then out to each light, 1 from correct row out and 1 return to earth row

  • Registered Users Posts: 8,239 ✭✭✭ Pussyhands

    So my theory was right. lol

    So I guess there's like...3 way joins to say connect the left brake light to the right brake light. Is it easy to use heat shrink for that or would another junction box be more common?

  • Registered Users Posts: 7,251 ✭✭✭ funkey_monkey

    Depending on the size of the trailer, you can get a proper junction box for the job used by Ifor Williams etc or you can use a std electrical IP44 or better rated junction box. I've only used the latter (IP55) when wiring lights.

    In most setups the 7-core cable goes back from the vehicle socket to a junction box on underside of floor. What I do is then take a length of 7-core from the junction box to the left rear cluster and one to the right rear cluster. Each cable will have common wires - earth (white), fog (blue), brake (red). The remaining 4 wires are side dependent - LH indicator (yellow), black (LH tail), green (RH indicator), brown (RH tail). So on the 7-core going to the LH rear cluster when I trim back the outer sheath I'd snip off the green and brown - as they are for RH and vice versa for RH cluster.

    In the junction box I'd do the same snips. It is then just a matter of connecting yellow to yellow, blue to blue, etc. The only additional effort is when you have front/side marker lights. They require connections to earth and the tail for that side. I'd normally use 2-core for that.

    Inside the junction box I usually use 2-way and 3-way Wago connectors. However, I've seen implementations using block connectors and a long rectangular junction box which works well too.

    I cable tie the wiring to the chassis where possible and only use cable clips if necessary and when I know the nail won't penetrate through the floor. Hammering in nails whilst lying under a trailer can be awkward and you will get covered in dust - so wear safety glasses to protect your eyes.

    It can get complicated when you go to connect your wiring at the clusters. Some have a wiring tail for you to connect to and others might have spade terminals and you'd need to crimp female spades onto your wiring. For example, I put some Brittax rear clusters onto a piece of machinery and its wiring was black, green, red & purple/green. However a quick Google and you get conversions. When they provide a tail I would usually use bullet terminals to connect the tail to my 7-core. Reason being that if the cluster got damaged it is easier to replace than if I soldered them together. I would then wrap with amalgamating tape to protect from weather.

    Another thing I do is to create a small loop of excess in the 7-core going to the cluster and cable-tie it to the chassis so that if I need to redo the bullet connections then I don't have to rewire from the junction box.

    Last night I was rewiring a small IW calf trailer that got the cable dragged along road after it fell out. The factory had run 7-core from each rear cluster up into the 7-pin plug bypassing the need for a junction box. Not sure how the spliced out the wiring for front marker lights. What I ended up doing was putting a 7-pin socket on the trailer and connecting both 7-cores into the socket. So there are two other ways to wire up, although my preference is always the junction box.

    In regards to the ground - should not need to do anything with the ground apart from match the pins. The ground used will be the ground on the chassis of the towing vehicle so that it is a common earth.

  • Registered Users Posts: 7,251 ✭✭✭ funkey_monkey

    Forgot to say, if you don't have the right tools such as a wire stripper, crimper, screwdriver set, etc then it makes the job a lot more laborious and frustrating.

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  • Registered Users Posts: 8,239 ✭✭✭ Pussyhands

    Great info! Legend!

    The ground attached to the chassis, is that just a wire from the ground terminal in the junction box welded onto the chassis?

  • Moderators, Society & Culture Moderators Posts: 12,319 Mod ✭✭✭✭ blue5000

    Pulled these from chit chat to make them easier to find in future. Thanks to all who contributed.

    FM what do you recommend to actually join the wires, are the screw connectors ok? What are you like on Fiat tractors? Only thing working on ours is the left indicator and starter. Headlights work when they are plugged in at the back of the light whether the switch is on or off. Don't know where to start looking.

    PH, I agree, a basic vehicle diy electrical course is badly needed, even how to use a multi meter videos on youtube get too complicated for me anyway.

    If the seat's wet, sit on yer hat, a cool head is better than a wet ar5e.

  • Registered Users Posts: 4,012 ✭✭✭ orm0nd

    if you want a permanent connection that wont give trouble in years to come, solder the connections and seal with glue coated heat shrink

    I have also thrown away the stupid junction boxes that IF insist on using and use soldered joints there, no more messing with multi meter at 6 am with a loaded box when you find you have no indicators

  • Registered Users Posts: 9,970 ✭✭✭ patsy_mccabe

    I rewired my Ifor Williams completely. It's fairly straight forward. You need special wire which is oil resistant. I also used IP60 rated junction boxes. I used wire ferules crimped onto thr end of all wires. Follow the attached wiring diagram. Remember that every light is essentially working off the battery when operated, so each bulb has a positive (+12V DC) and an earth.

    The White is the common Earth. I don't think you connect any earth to the trailer body. I didn't anyway. It's get confusing when you buy a set of back lights and they both have the same colour wiring. You just change the Left/Right configuration. The yellow wire (left indicator) is treated as if were Green (right indicator) when you put it on the right hand side.

    What caught me out as well is, with a detachable wire with 2 plugs on the front, you wire one plug, the mirror (left to right) of the other. Makes sense when you do it.

    Post edited by patsy_mccabe on

    " Always keep your eye on the ball, even when its in the refs pocket"

  • Registered Users Posts: 7,251 ✭✭✭ funkey_monkey

    Screw connectors (block connectors) are fine. They can loosen over time, but as long as they are nipped up tight then the chances of them loosening are slim. I have a preference for Wagos as they are simple and maintenance free.

    I normally use this type of junction box as I have them lying around for electrical work and usually can't wait to get in a 'proper' box:

    I have soldered & used heat shrink too. A lot of it is down to preference and what's available at the time. If the joints are done correctly and the junction box is correctly sealed then it will last a very long time.

    You can get junction boxes specifically for this work:

    This Britax one is the type used by Ifor Williams. I'd consider using something like this if there were additional marker lamps on side/front and/or internal lights as with increased number of wires it can get messy very quickly.

    Wiring up from fresh and maintenance/fixing are totally different. It is not something that I do a lot of but when I do the fault is usually corrosion on the connections/joints. Sometimes it is the wiring itself, although inspection usually shows easily if it rubbing and worn through the sheath and easily fixed.

    I would not be sure why your headlights are staying on but it is likely to be either the switch or possibly the headlight relay (if there is one). I've not come across many shorts to positive but it is also positive.

    I'd start with the switch and see if it is working okay using the continuity setting on a multimeter or wire up a lamp and battery to it.

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  • Registered Users Posts: 1,256 ✭✭✭ hopeso

    Is anyone using the 13 pin plugs? I changed all mine over years ago. I find that they’re a far more reliable connection at the plug/socket and I have reverse lights on the trailers. Going a bit off topic now, but does anyone know what strength LED floodlight I could replace the standard reverse lights on the trailer with, without overloading the wiring?

  • Registered Users Posts: 7,721 ✭✭✭ FintanMcluskey

    What are you like on Fiat tractors? Only thing working on ours is the left indicator and starter. Headlights work when they are plugged in at the back of the light whether the switch is on or off. Don't know where to start looking.

    Despite the poor reputation of the circuits, normally all gauges and lights work on the fiats (although usually the lights are dim)

    The original headlight switch carries the full circuit current, as opposed to only switching a relay. This causes the dashboard connections to overheat and eventually breakdown.

    Brewster electric in Lanesborough has a modified headlight relay kit pre-made for the Fiat's, which connects the headlights direct to the battery and then the existing loom is then only used for switching the relays on/off for the headlights.

    In your case it sounds like the headlight switch has failed on, or perhaps some wires have fused together. A simple test to diagnose the switch is to plug out the switch under the dash and see do the headlights extinguish.

    Those youtube tutorials are unnecessarily complicated sometimes. a simple DC light tester is a great way to start understanding circuits.

  • Registered Users Posts: 7,251 ✭✭✭ funkey_monkey

    I've switched over a jeep to 13 pin as it was always releasing the plug. Far more secure and better connections.

    It depends on the thickness of your wiring as to the current rating. I've seen current ratings from 5A up to 16.5A. Some have a thicker white (earth) wire rated up to 25A. If you cable is relatively new it might be stamped along the sheath, although I don't recollect seeing it on any cabling I was using. As it is a 12V circuit you should get something more powerful easily enough:

    Power (Watts) = Voltage (V) x Current (A)
                  =   12        x     4
                  = 48

    So, assuming you don't draw over 4A then you should get a 48W LED light. You also need to ensure that there are no other loads on the circuit (no other lights powered by the reverse) and maybe check what the fuse rating is in the towing vehicle for the circuit if you can to prevent blowing it by attempting to draw too much current.