Hi all,

My rear interior light won't work at all. The front one is working absolutely fine. I've changed the bulb on the rear light, disconnected the wiring on both lights, inspected and re connected. I can't see any obvious problem, nor can I find a forum thread for anyone having a similar issue. I have the bulb dome type interior lights - non-LED. It's an Ecoboost Zetec 2014.

Anyone got any ideas? Many thanks in advance!

 

 

Maybe an issue with the fitting itself? Can you swap the front & rear lights to try and test the theory? 

I agree John, I told him to do that 5 hours ago in the other thread he has running - not bad for a guy who just joined and has only made two posts both for the same thing.

7 hours ago, cx7117 said:

Hi all, sorry to hijack this thread - but I am having a similar issue.

My rear interior light won't work at all. The front one is working absolutely fine. I've changed the bulb on the rear light, disconnected the wiring on both lights, inspected and re connected. I can't see any obvious problem, nor can I find a forum thread for anyone having a similar issue. I have the same light type as Albacore posted earlier in this thread.

Anyone got any ideas? Many thanks in advance!

 

Indeed. However I realised shortly after my initial post that I was better to start a new thread instead of hijack an old one. Forgive my ingenuity, I'm new to these forum fun and games.

No go on the swap over unfortunately. They are different light fittings with different plug / socket arrangements for the wiring.

It may be time to look on ebay or at car breakers local to you for a replacement then, just incase the unit is faulty

Just bought a second hand unit on ebay. Fingers crossed that sorts it.

Fingers crossed that sorts your issue out mate

No joy unfortunately. Neither unit works. Swapped bulbs around, cleaned and accessible elec connections, unplugged and cleaned the front light unit also. Anybody got any other ideas? Anybody else had a similar problem?

Sounds like there may be an issue with the wiring itself, maybe a break in it somewhere??

The rear light is controlled by the front unit. I would be checking that the front unit is sending the signal to the rear. It looks to me like pin No.3 on the connection for the front light is the one that's providing the neutral to the back light. In other words, its switching the neutral not the live.

You could test this with a multi meter. I'll take mine out tomorrow and test it to confirm and report back. 

Also, does the light in your glove compartment work? There is a fuse F60 (think this will be in you BCM). 

12 hours ago, Nathan Buffery said:

its switching the neutral not the live

Looking at the diagram both bulbs are switched to ground (not neutral, that's mains). It's a common way to control loads with transistors.

23 hours ago, mjt said:

ground (not neutral, that's mains

Neutral Smeutral!!! 

So tested the connection this morning and I can confirm that pin No. 3 on the front light is a switched earth. No.1 is the live, No. 2 is a variable earth that decreases in voltage to dim the light and No. 4 is the earth. 

Mine has never worked properly since I've owned the car. I found the fuse had blown, and when I replaced it, it doesnt dim down and instead just stays on. I've swapped the front unit out with another one, but it does the same.

All other convenience lights are working. Boot, front, glove box, all good.

Will dig out the multimeter, try to remember how to use it and have a go tomorrow.

So on the rear light, you'd be looking for a live on the white and brown wire, and earth on the blue and white wire when the front light comes on. The live on the white and brown should be present all the time. Its fiddly, so you might want and assistant to hold your multimeter.

Thanks Nathan.

So... I got a steady 12V live on the white and brown wire and a steady 12V live on the blue and white also, even with the front light switched off. Also testing the continuity of the blue and white wire back to the front unit gave 0.02 ohms. Hmm... short circuit problem? Any ideas?

Potentially related: there is a bit of minor blue copper corrosion on the internals of the forward unit, and this focus did have damp problems before I bought it due to leak into boot. Hmmm...

What condition was the light unit you got from ebay was that all corrosion too ?

40 minutes ago, cx7117 said:

I got a steady 12V live on the white and brown wire and a steady 12V live on the blue and white also, even with the front light switched off. Also testing the continuity of the blue and white wire back to the front unit gave 0.02 ohms

Assuming you were checking continuity between the front and rear connectors this suggests an open-circuit somewhere inside the front unit. The 12V you see on both sides of the rear bulb is due to there being no current flow and therefore no voltage drop across the bulb.

The corrosion is on the front unit. Both rear units (the original, and the ebay purchased) seem in good condition visually - difficult to believe both could be faulty.

I guess the next course of action is to purchase a new front unit?

I can see at least two of the 'plated through holes' on that photo that have totally corroded. It would seem very likely that you have found the fault and its the front unit that needs replacing.

It a pity we live so far apart as I have a spare front unit. You would be welcome to it, but I'm unsure if it works properly due to the dimming fault I have. 

@mjt& @unofix you dont happen to know if it's the BCM that dims the light? Or is it done through the 'logic' board in the front interior light? 

8 minutes ago, Nathan Buffery said:

you dont happen to know if it's the BCM that dims the light? Or is it done through the 'logic' board in the front interior light? 

that's a very good question and to be honest I don't know the real answer.

My guess would be it's controlled by the BCM. I make that assumption based on the fact that all interior lights - front - back - footwell (if fitted), all fade out at the exact same time.

That's bad news for me then. I dont suppose you know if it's a component within the bcm that could be swapped out? Looking at the wiring diagram, it looks like it's a separate unit. 

I also don't know but since you said the signal on pin2 is variable and decreases as the lamp dims that suggests that Unofix's assumption is correct.

I have spotted that there are 2 dimming circuits. There is one for the ambient lights, which I dont have (yet). So I think I'll have a go at swapping the pins across at the BCM.

@cx7117 if you PM me your address, I'll send you the interior light.