Hi, I'm looking for some help and advice on how to fix a problem with the boot / luggage compartment lights not working on my 2017 mk3.5 focus estate.

I've removed both the left and right hand light fittings, and the 5w5 bulbs are fine. I am getting 12v between the Brown/Green wire of the bulb connector and a ground point on the chassis, on both light fittings. I am not getting continuity between the white/blue wire of the bulb connector and a ground point on the chassis, on either side. This is with the tailgate open.

Things that ARE working:

1) Front and rear passenger interior courtesy lights come on when doors are opened.

2) Glove box light works

3) When tailgate is opened with ignition on, I get a warning about tailgate being open.

4) Double pressing the key fob tailgate open button unlocks the tailgate

So fuse F60 is working fine.

If I leave the bulbs in the fittings, and run a jumper wire from the white/blue wire side of thr bulb connector to a chassis ground point, with the tailgate open, the bulb lights up on that side. This works on both sides.

If I understand the way this should work, it's the BCM which switches the ground to the luggage compartment light fittings when the tailgate latch mechanism reports that the tailgate is open.

I've taken the tailgate plastic cover trim off, and between the tailgate latch mechanism connector's white/blue wire, and either of the luggage compartment light fitting white/blue wires, there is continuity, so the tailgate loom passing through the rubber boot is fine.

So I'm currently thinking there might be a break in this white/blue from both sides (or if they splice together,) and the BCM. Or the BCM isn't grounding this wire when it gets the tailgate open signal from the latch mechanism.

I don't have any wiring diagrams, so I'm really looking for some help either with links to wiring diagrams for my year of Focus, or anyone that has had a similar issue and resolved it. Thanks in advance!

Edited March 7Mar 7 by SSD
Missing info

I think I may have figured this out. I found an online wiring diagram for the 2015 model estate, which actually shows that the BCM is switching the +12v on the Interior Light Relay, which goes to the Luggage compartment lights, when the tailgate latch sends the signal to the BCM that the tailgate is open. This part is working correctly as I am getting +12v on the Brown/Green wire going to each bulb.
When the tailgate latch is open/ajar, the internals of the latch should ground the white/blue wire coming into its connector on pin 4 (C4223) from the lamps through to the black/white wire on PIN 2 (C4223), which then goes to chassis ground. This appears to be what has failed. If I insert a short jumper wire between pins 2 and 4 on the tailgate latch connector (C4223) with the tailgate open, the lights come on.
Pin 2 of C4223 has continuity to ground, so I know the black/white wire to ground is intact, so it must be the latch internals that have failed. It doesn't look like it's easily opened up, so no doubt it's a non-serviceable item, so a new tailgate latch sounds like the answer.

Just to add to this - a replacement lock mechanism did indeed fix the problem, and the boot lights turn on correctly now.