That does make sense on the 3 wire setup i agree.... so i thought i would dig out a schematic.
This wiring pic shows the 3wires and as Deaky said, it shows:
br - (brown) - 639 earth point left a-pilar
br/rt - (brown/red) - B533 connection 1 main harness (BCM switched neg) connects to B129 to B264 to A144 to T73a/4 (J519)
rt/sw - (red/black) - B250 positive connection 1 main harness (BCM timed +12v) ( 7.5A fuse 24 holder C) to B323 to T73a/66 to (J519)
So it looks like the BCM (J519) is ultimately controlling the (BCM switched -ve)(T73a/66) side and also the (Timer switched +ve)(T73a/4 (J519))
from what i can see on Elsawin.
View attachment 27647
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here a snapshot from a later van with LEDS, but my German isn't that good. Its seems that the +ve supply and -ve ground are from B533 & B250 (translates to connection in roof loom)
again we have a similar setup,
br/rt - (brown/red) - B533 connection 1 main harness (BCM switched neg) connects to B129 to B264 to A144 to T73a/4 (J519)
rt/sw - (red/black) - B250 positive connection 1 main harness (BCM timed +12v)( 7.5A fuse 19 holder C) to B323 to T73a/65 to (J519)
So it looks like the BCM (J519) is ultimately controlling the (BCM switched -ve) side and also the (Timer switched +ve)
from what i can see on Elsawin.
View attachment 27645
so unless im reading it wrong The BCM deals with both the switched +ve and -ve and both old and new versions on the circuit. I suppose its also monitoring the circuit for bulb defects and faults etc.
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Also regarding the BCM timed lights, here is a clip showing a relay under the dash by the BCM, its unconfirmed yet whether its fitted to our van.
2a - Interior light relay -J602- (646)
View attachment 36698
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Additional info provided by
@mmi
Slightly diverting from the original post but thought might be useful add here for future queries/upgrades.
As
@Dellmassive mentioned new LED lights in rear roof lining are connected with 2 wires.
And indeed the LEDs do not come with a switch so they stay always on (up to 60 minutes) when a door is open. Current draw is about 0.2 Amps (@12.2V). I think that light output is definitely satisfactory. The color of the light is approx. medium white (personal opinion, compared with so called warm white and cold white LEDs).
The frame is 137 x 67 mm. The opening in the roof is 129 x 54mm. The light requires 17 mm of depth (from the roof surface). It has three bars of light (yellowish bars in the picture).
The light has a product code 7E0 947 123 A. The connector on van side has a code 1T0972703. Can’t confirm if the LED would be a plug and play with the wiring of an “old”…
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