Hi everyone. Is there a point in the electrics of the car, that I could connect to that would either sit at 12v or earth depending on whether or not the car was locked or unlocked? I have a circuit in mind to partially replace or compliment the BCM's control of the locks (rather than fit a new BCM), but it needs to reflect the status of the central locking. Everything I can find is pulsed and used to change the status. Is there a latched voltage anywhere that my circuit can read/use. I can use a latching relay but if there is such a point I could simplify the circuit I want to add.

Everything on your 2018 Focus is controlled via the Canbus network. Data is transmitted on the Canbus and is read by which ever module the information is for. When the you lock/unlock the doors a message is sent from the BCM to the Drivers Door Module (DDM) to tell it to operate the door lock.

What you are trying to do is break in to a data network and control or read the information as a simple 12V signal, which is not something that is possible.

Hello again unofix, more like read an address in the BCM somewhere. A rabbit hole! Thanks again!

There is a tell-tale lamp in the lock/unlock switch on the driver's door casing (I think), maybe you could tap into that?

HI Dave, Yes, I noticed that light on my search. I locked the car and came back later for a look. Unforunately it doesn't stay on until the car is unlocked again. I found what I was looking for though. The drivers door latch has an unlock wire that is not implemented by the other door latches. Using the schematics (thanks again unofix) it goes back to pin 55 of the BCM.

23 hours ago, unofix said:

Everything on your 2018 Focus is controlled via the Canbus network.

Treating the BCM as a 'black box', it has inputs and outputs that are not digital and are fair game. This input to the BCM on pin 55 is tied to ground by the drivers door lock, when it is unlocked. When the car is locked it sits about 11-12V, what someone I read called a floating high, waiting to be pulled low.

This was the missing piece. The boot was popping open whenever I unlocked the car, sometimes when I locked it too. My assortment of relays and wires has taken over the boot open/lock funtion. For me it's a win if not a complete fix.

Thanks for your suggestion. I've posted the full thing under 'Boot pops open on unlock'