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Cannot manually turn on rear interior light on 156

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So, as the title says, when I open the doors all the lights illuminate, as they probably should, but I cannot turn them on when I'm driving for example. What could be the problem? Sometimes one of them does start working randomly...
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Alfa Romeo 159 JTD 8v (2009)
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If I remember rightly, push the light lens and they cycle through being on permanently, being on only when the doors open and never on, doors open or not. Just remember not to turn them on and leave them on - you might find the car a bit harder to start after leaving them on overnight.
 

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Discussion Starter · #3 ·
I know, but this is the problem, I cannot switch them on, nothing happens. The only time when pressing them does anything is when they're on by timer (when opening the doors for example).
 

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Discussion Starter · #5 ·
Yeah, I have to pull the headlining off (again!) anyway. It's wrong for the year and a bit tatty...
Anyway, this is what eLearn has to say:

They are switched on via a direct earth signal (permanently activated) or a signal coming from the integrated services control unit M40 .

Since the part with the integrated services control unit works I'm assuming I have to get an earth on one of the pins which should be easy enough? The wiring runs pretty close to where I was grinding the floor due to rust around one of the flaps so it is possible I've disturbed something there...
 

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I have to admit to have never ever needed to put on the rear interior lights...come to think of it....even the front interior lights.
I know this may not help....but do you really need these to work ?
 

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I have to admit to have never ever needed to put on the rear interior lights...
I only ever did it once. I needed to get some stuff out of the back in the dark...... I then forgot to turn it off... :cry:
 

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Discussion Starter · #12 ·
Well, got the headlining off so I tried fixing the lights but I'm thoroughly confused now.
I measured the input with multimeter and it seems to be like this

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That would mean the switch inside the light should switch between left and right connection so that when the door is closed it would switch to the right earth and light up! But when I measured the resistance there only seems to be a connection between middle and left or nothing at all. I also removed the switch and same thing. There is never any connection between middle and right pin!

Finger Electrical wiring Cable Thumb Engineering


Are all my switches bad? I would appreciate if someone with working lights or some more knowledge can help me clarify this :)
 

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The terms you use to describe voltage are incorrect which is perhaps making it harder for you to understand. Think of a battery. There is what we term a potential difference between positive and negative terminals. Open circuit is nothing at all. Going on that, your first picture describes a situation where the light won't work. Sometimes using electronic tools makes it harder to understand. Terminal 1 in 1st picture shows 12v +ive because the bulbs are in. With bulbs out, there would be nothing. Bulb filaments make a circuit.

From the left your terminals are as follows:
1. Switched earth (12v -ive) by switches in door latches. This is working.
2. Positive supply (12v +ive). This is working.
3. Permanent earth (12v -ive). The circuit needs this for the individual lamps to be switched on by operating them. This is where the fault is.

I do not know where the fault is exactly. However, it would be easy to take a spur from the permanent negative in wires going to the front courtesy lamp and connect it to the wire of one of the rear lamps. You could trace the wires for the rear lamps but I suspect it is not a separate earth for them. It would make more sense that there is a common earth and the earth wire to the rear lamps has become open circuit (broken wire/corroded wire/heavy oxidation at junction).

When I had that fault, I was lazy and just took a spur from a good earth. That car was not a keeper which would last so no need to do it properly.
 

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Discussion Starter · #14 ·
Actually the permanent earth works fine. There is always 12V between middle and right terminal, there is just never a connection between the two in the lamp, that's why I suspect the switch inside the lamp. If the lamp was to light up with the doors open when the left terminal gets 12V that would mean the permanent earth would have to be the middle (common) terminal. Which is not... Left terminal actually becomes earth and when it deactivates it's likely an open circuit.

Position for the doors open light
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This should then be the path to light up during driving...

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If I bridge the terminals it works...

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But that would mean not one of the switches out of the five I've tested, works...
 
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