The interior light does not turn on when opening the driver’s door. It does for the passenger door.
I’ve tested the switch - both sides are the same, switch is open when door is closed, switch closes when door is open making the circuit through ground on the door frame and (in theory!) turning the light on.
Passenger side has 12V on the switch wire. Driver’s side has 0.5V.
Something’s popped somewhere but as they appear to be on a common fuse, I’m at a loss for what it might be. Any thoughts?
The wire could have a break in it, so running a separate test wire from one end to the other would check for that.
You say you have tested the switch. How have you tested it? I would be checking for corrosion causing a poor connection and checking for stickiness in the switch.
How good is the connection to earth?? Check for corrosion.
@Greem
Your assumption in the way it work is spot on.
If you’ve had the wire off the the terminal on the switch and only measuring 0.5v, then there has to be a break somewhere.
However, with the switch being in the side pillar, there would be no moving wires, so how this has broken is anyones guess.
My first plan of attack would be to pull of the sill kick plate and start tracing the wire back the best I could.
@999to5 I’m reasonably competent with electrics - I took the switch out and bench tested it, it closes and opens as expected. I continuity tested the switch to ground, and the grounding on the door frame, that’s all good (no corrosion evident, no resistance when switch closed etc). I then checked the supply voltage and there’s basically nothing there.
@Keat63 I’ve had the pillar trim and sill trim off; the wiring goes the other way toward the middle of the car - into a loom with what I think is the PRHT and seat belt tensioner wiring, which I suspect goes into the loom through the centre console.
I’m beginning to think that it’s actually the sounder in the instrument cluster that’s failed, as it would make sense for the circuit from the cabin light to drop to the sounder before going to the door. If that is the case then that’s a garage job.
I’ll just have to put a reminder sticker on the steering wheel!
Is this something new or has it always been the same?
If its something new, what might you have done that could affect it??
I was once told by an auto electrician that it’s very common for owners to screw self tappers into sill trims etc and catch a wire.
If you are getting 0.5v, could that be consistent with most of the current being diverted by a short-circuit to earth but some of it still making its way along the wire??
If that were the case then the light would be permanently on as there would be a circuit, hence me thinking something has popped. If only I could find an actual wiring diagram for a 2014 NC PRHT!
I had a whole lot of electrical problems with my MK 3.75 when I first got it. Turned out to be corrosion on the pins of connector leads that connect slave servers to the main server. Once that was replaced (by the garage - special tools are needed) the problems disappeared. May not be the cause of your problem, but something to remember
I still haven’t traced the problem. I’ve had the trim off the windscreen and followed the loom but can’t see where the wiring goes - at least part of it goes to the ECU and/or alarm system.
Fairly good shout on a corroded contact, if only I could find it!
Have had the car over at Thrussington Garage today getting new Kumho PS71 boots put on all round (after finding a few weeks it had run-flats fitted at the rear when I bought it…).
Mike spent some time having a look at the electrics for me, and agreed that the wiring itself is all good from the door switches, through the rear panelling and into the loom that traverses the transmission tunnel to the front of the centre console (pointing out that if there was a short the light would be on all the time, which seems fairly obvious now I think about it!). Unfortunately that was all we really had time for.
Next step will be to get the full wiring diagram for the car (which seems to be about as common as a fish with legs) and trace all the components. It looks like it could be a faulty contact with the Body Control Module, or a failure of that itself.
I have checked mine today and I have power to the driver’s side switch but still no light. Passenger side works find but even if I change the switches round, nothing.
I know this question get’s asked all the time but have you ever had the passenger side footwell wet from the scuttle grommet leak?
Numerous instances of short circuits and issues from the fusebox getting wet. Have you had the footwell fuse cover and plastic surround off and checked the fuses and contacts and also the earthing points and wire bundles associated with them.
As far as the module which controls the interior light, key illumination lights on warning etc it’s very possible that is faulty or has been damaged due to previous water issue but without access to wiring diagrams locations etc who knows. Perhaps someone who has broken or stripped these cars for track use could help with that
