First allow me to paint a picture, I have a MK3 2013 1.6tdci Zetec S which i use as a second run around car (as i got it cheap due to it being a cat D its nice enough but its a bit boring as i also have a 2015 ST Estate Replica which i built last year as i needed a cheap estate for work and the standard one look boring, last month along comes my rather unfortunate friend who decide the best place to park his 2015 ST which he had owned for a total of two weeks was sideways into a rather large tree at about 60mph....don't worry he was fine the car not so much...as he's third party only (don't ask, hes an idiot) he was left with a hell of a mess which i bought for £1500 absolute bargain i know.
So here I found myself with a load of ST parts to play with so sold what i didn't want and decide the best place for most of it was on my Zetec S, as id seen a few face-lift upgrades i thought why not. all pretty easy fitting the panels / bumpers / interior / trims etc (those that were salvageable) but found when i put the headlights on they came up with a lo-beam error message on the dash and none of the lights actually worked.
Well after many searches on all the forums and being told on here that i would need to get ECU's / software upgrades or coding to get the MK3.5 headlights to work on a MK3 i decided not to take anyone's word for it and have a go myself and hey presto £40 later and there fully functional without the need to do any software upgrades or buy any ECU's
luckily i was emptying out the garage and in skip had a pair of 2012 smashed headlights from a previous cat D i had fixed a sold a while back so decided to strip the light looms out and marry them up against one from a broken 2015 headlight i also had going into the skip.
the only difference between the two looms was the MK3.5 has another connector so looking from top to bottom left to right we have
MK3 = 1: aim adjuster / pin 2: aim adjuster / pin 3: low beam / pin 4: low beam to indicator & Main beam to sidelight / pin 5: aim adjuster / pin 6: indicator / pin 7: main beam / pin 8: sidelight
MK3.5 = pin 1: aim adjuster / pin 2: aim adjuster / pin 3: low beam / pin 4: low beam & indicator / pin 5: sidelight & Main beam / pin 6: aim adjuster / pin 7: indicator / pin 7: indicator / pin 8: main beam / pin 9: sidelight
so i got to thinking, no internal ECU, no high tech things inside the light unit surely all they did was reconfigure the loom, and rather than cut into the existing loom (in case i was wrong) i purchased from ebay a set of 2015 headlight plugs from a damaged car (cost me £40 which was a bit steep but everyone seemed to want to sell me the whole loom for £100 so £40 seemed a better option)
3 days later and the plugs arrived
so out came the tool box - all you need is:
2x headlight plugs from 2015 / 2016 focus
2x headlight internals removed from 2011 to 2014 headlights
heat shrink & either heat shrink cable connectors and crimping toll or soldering iron - (depends how you want to go, some prefer to solder the connections i decided heat shrink connectors plus additional heat shrink over the top would be better)
wire stripping tool
optional cable tidy / tubing depends how you want it to look once complete
so i found the easiest way to wire them without getting mixed up is to plug the two plugs into each other and solder one at a time following 1 to 1 - 2 to 2 etc then when you get to the missing wire in block 4 take the lower cable (as two wire come out the MK3 headlightlight loom) and plug it into number 5 and continue on (hope this makes sense)
new 2015 plug bellow - mine also had an addition green and orange wire (bottom left) which is for the DRL - but as i wasn't fitting them yet I left it there unused
plugs plugged together - mid wiring
after about 20 mins your left with this:
unplug and tidy with some insulation tape and if you want it to look good some cable tidy (i used the stuff that was on the loom/plugs i was sent - i was a tight fit but looks a lot better - bellow is half way through the tidying process)
20 mins to do the other side so a total on about 40 mins or an hour if you stop for a beer like i did and you have two connector plugs/looms for 2011-2014 to 2015-2016 headlight
plug into your existing loom one end, then the other end into your new face-lift headlights and hey presto working 2015 face-lift lights on a 2013, with no error messages or coding required
now this may also work a lot easier if you just take a feed from plug 4 and run a new wire into plug 5 (from the first two pictures) on your existing loom but i didn't want to try this in case it didn't work and if you wanted to change it back at any point with these at least its a plug and play option, again if you can find a breaker willing to give you the plugs you could do this for next to nothing.
the lesson to be learnt is things are not always what they seem, sometimes if you have the confidence to give it a go it may just pay off.
just as a little disclaimer, if you do this its at your own risk, these work 100% for me but if you do it wrong and it doesn't work i give no guarantees