do yourself a favour. but the lights with 9 metres of leads. that way you cun run the leads all the way to the plug or junction box without joins. 90% of faults will be in the joins or the earth wire at the plug.

Ok .. 40 odd yrs trailer wiring, underground ethernet, pho0nes, cable to water pump in the garden pond... list goes on

 Lot failures.. anfd this is what works fot the last 25 yrs.. including the phone ethernet trailers... and pond
 
 Get a off cut length of heavy duty  240 extenstion cords lead.. about 10" long.. strip out the internal wires leaving a tube.
Thread you cable thru..and slide out of the way
 solder the wires.. but offset them a little.
 Quality insulation tape around.. 900V 3m.. over lap 1/3   2 layers.
Now smear bathroom silicone over the join and build up at the end the lead cable tube is.
Start sliding the tube over, packing more silicone in and give a little twist as it goes on.
 Force in more from each end
 3 layers  1/3 over lape quailty insulation tape, stretched up tight.
 Do not move for 24 hrs.

 The connection to the car.. solder the ends of the wires, put into the connector.. check all the wiring is good...fill the connector with silicone, and screw on the lid.

 Bit unconventional..  over kill, but it works forever.
 Have extra length for the connector thu.. one day you will forget to plug it in , or run over it , forget to un plug, and break it... extra length allows to simply chop it off and replace.

 I run trailer cables inside box sections where can.. they cant be rubbed , banged, crushed,  damaged.
 Cable tie each end, so no stress can be made to the cable in the box section , or any connections.

 The only hasstle is I ever have with my trailer lights, boat or the others is occasionally need top spread the connector pins 1/4 mm for good connection.

 

So I’ve wired a couple of trailers and fixed a couple for mates (I’m a industrial sparky by trade – a long time ago…)

 

 

 

I applied the same as what I would do for cable jointing in wet or underground.

 

 

Get yourself some 3m glued heat shrink, 3:1 shrink ratio, for going over the outside of the total cable, make sure it goes past the stripped section by 75-100mm on both sides of the finished joint area.

 

Don’t try and make the jointed area to short.

When you join the individual wires, don’t make them the same length, stagger them so the joins are not in the same place, ie from the stripped out cover, cut the green at 40mm, red at 60mm, etc… The reason for this is it makes a smaller diameter joint and also makes it a bit more flexible for resistance to vibration wearing.

 

Put smaller heat shrink on to the wires, again make sure you have a decent over lap for the actual stripped copper bit, 20 mm each way.

 

Strip the internal wires. I would suggest about 15mm

 

When you join the copper, lightly twist both together (make sure you have clean fingers while doing this, ie keep the copper as clean as possible – it makes it easy and better to solder), and solder. Best way is soldering iron under the wires, and ‘walk’ the solder from the iron onto and around the wire – you should end up with the solder being on the top of the wire while the iron is under it.

It will sort of suck into the joint – hard to describe, you’ll see it happen though, it means the solder is right through the joint. The joint shouldn’t have any ‘blobs’ siding on the bottom and should be smooth looking – no copper sticking out or solder sharp bits.

 

Then shrink the internal heat shrink and slide down the outer glued heat shrink and shrink down.

 

Over all joint area should be around 200mm and outside heat shrink around 350-400mm

 

 

If you want to get really into it, you can wrap the internals with self amalgamating tape before the out side heat shrink gets shrunk, but three is a bit of a knack getting that correct – ie you need to put it between the internal wires as well as around for it to actual do anything, and can/does make the joint slightly bigger. I would personally do it though.

 

 

I haven’t ever heard of any that I’ve done this way crapping out. Doesn’t take to long to do either.

 

And as above, certainly solder the 'tails' that go into the screw connections in the plug.

 

And if you have some of the heat shrink from the above joint (the outside glued stuff), I'd use a 100-200mm section right on the end where it gets clamped in the plug down the cable. will stop the outter cover being pulled away at the plug

 

 

I have long used normal non insulated crimps, on tinned wire, heat shrink on them and one big one over the lot.
Self amalgamating tape is brilliant if used properly. I have pulled up bore pumps, 30m underwater with amalgamating tape on them, still fine,
Silicone grease or vaseline in trailer plugs.

Great job  - and the bonus of satisfaction at getting it done properly at last.  (if you are like me still wondering why it wasn't done right first time ) and now you know what a good job looks like - good to know with boats!

Gary Roe wrote: Excuse me, I have a problem with my led trailer light. Wired and installed these and everything works except no constant running lights. Brakes and blinkers working but that’s all. Any suggestions?

"Constant running lights" - do you mean the orange lights normally mounted on the front of the mudguards?

when replacing old lights tie a bit of string or flexi pipe to the wires running from yr plug easier to feed them back that way