Electrics - How does this light/button work?!

[vantastic]

For context, I'm converting a Crafter to a camper. I have a bed over garage and I want to reroute the interior light to the garage so it comes on when I open the doors. I have already installed LED strips in the garage so all I need now is some electrickery to make the magic happen. I thought this was going to be relatively easy so I have buried a 2 core cable in the walls already to where I can join with the vehicle loom.

But this is where I ran in to some trouble. I assumed the interior light would have 3 cables coming in but I have 4.

This is where my knowledge is starting to fail me. Lp1 is a permanent live. It gives a reading of 12v against the chassis at all times. It's a red cable so this one I'm sure of. It is always connected to the bulb but it is also switched. G1 and G2 are gates. If both are left open the light doesn't come on at all. If G1 is switched allowing a connection to EIN then the light is always on. If G2 is switched then the light is only on when the doors are open.
The voltage between Lp1 and TK/EIN is always ~8v
Lp2 is the other side of the light bulb. No switches or connections to anything else. The voltage between Lp1 and Lp2 is either ~10v or 0v.

Having figured all of this out I thought, if I just join Lp1 and TK on one pole and Lp2 on the other I should be able to use that to my lights, but no. If I join them I get ~12v but then when I close the door it drops down to ~8v. 8v will still drive my LEDs. I'm pretty sure 8v is also enough to flatten the battery if it was left like that.

I'm stumped!

 

[Richard n Ann]

Solder your 2 core cable onto each side of the bulb holder and then down on to the LED strips, observing polarity ?
? Or have I missed something ?

 

[vantastic]

Well I want to get rid of the button completely. I don't want to have to bury it in the walls somewhere.

 

[tonyidle]

Use LP2 & EIN. Better yet obtain an LED light & use that instead.

 

[rod_vw]

Your light is not directly controlled by the switches in the light unit, they only send +12v on EIN or TK to an electronic unit somewhere in your vehicle.
If (and from your pictures & diagram I cannot be sure) the switches are mechanically arranged so that only one can be made at any time you could remove the complete unit and fit another switch to provide the same contact arrangement elsewhere in the vehicle and connect your new lights between LP1 & LP2. Observing polarity if the new ones are LED.
However you may find that LEDs do not work as expected due to the fact that they draw considerably less current than normal bulbs and the electronics of your vehicle may not 'see' them correctly. In my VW the OEM interior lights have both delay and fade characteristics which are not conducive with some types of LED bulb or strip.
If I were you I would do as suggested above and connect the new LEDs across the existing bulb holder with the bulb removed and see if it performed correctly before going to the trouble of re-wiring as I have described above.

Caveat - Please take all the above as a suggestion only, I cannot guarantee its suitability or success.

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[vantastic]

It does have a delay and then a fade, that's right. I've cut the wires and I'm using a multimeter to test so you could be right in that the ECU controlling the lights expect a certain feedback in order to operate as expected, my multimeter is not showing the characteristics of a bulb so the ECU isn't turning off the power.

I'm certain from looking at the switch that Lp1 and TK must be joined on the positive side and then Lp2 on the negative side. I'll try to wire that up to my LEDs and if it isn't working I'll try an incandescent bulb instead to see if it works then. I may need a resistor in line to compensate for the LEDs.

 

[Richard n Ann]

The latest LED strips I bought are quite power hungry. 1 amp per half metre so that's 12watts.. Are the festoon bulbs usually 10w? ?

 

[vantastic]

Ok so I connected the cables (Lp1 & TK) to positive and Lp2 to negative on my LED and it's all gravy! It's dimming the LEDs and everything, just like the incandescent bulb.
I'm getting a reading of 6v across the poles with the lights off. The LEDs range is from 5v to like 40v or something like that so the computer must be giving enough power to sense if there's something connected but not enough to actually drive it. Interesting!

 

[rod_vw]

Sorry vantastic I missed the fact that you have a Crafter, unless you have a New Crafter your electrics are a mixture of VW and Mercedes. Maybe a word on the Ross-tech forum would provide some insight into what is happening.
You may find all the wiring diagrams that you need at Broken Link Removed both generations of Crafter are available on there if you search down the page.

 

[vantastic]

Cheers for the links Rod! I had a quick look at Ross Tech and I think people there might know the answer to my next question on this topic.
I didn't have the workshop manuals either so thanks for that.

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[Vipar]

Is there a Ross-Tech type forum for Peugeot ?