Interior lighting delay

[Jimm]

Hi, I think I originally posted this in the wrong place, hence the new thread. I'd be grateful if someone with more knowledge than me on interior lighting could assist please. I am replacing the 2x original load bay lights with LED courtesy lights and a genuine VW step light. I did the step light a while ago, works fine. I then added an LED above the sliding door, on a 3-way rocker switch (to retain the on/off/door functionality). See badly drawing wiring diagram of my mods, attached. When I open the door, the LED comes on at the expected brightness. Last night when I fitted it, it came on for around 30 secs, then dimmed-off, along with the step light and cab lights. When I switched it to 'on' it came on but very very dim, unless I did this within 30 seconds of opening the door, whereby it was very bright. I also found that if I turned it 'on' (dim) then briefly touched the original filament bulb across the connections to the new LED, its brightness increased dramatically. Might be worth noting that at this point, the engine battery was pretty low and I had not put the key in the ignition at any point during the installation. May also be worth noting that I had to use the negative from the chassis, rather than the loom, due to inability to route all of the cables through pop-top surround. I thought this might be a resistance-sensing thing...... however.......
Next day......
I drove the van to work (45mins) and found that after this, the LED came on at the expected brightness, in both switch positions. The timer delay however had now increased to around 10 minutes, until the lights all dimmed to off (which from reading this forum seems normal) so all appears to be ok....

Any ideas?!

UPDATE: I originally wrote this 5 days ago and nothing has changed since, so all working fine but curious as to know what changed overnight, incase there is a nasty surprise lurking still......

I plan to fit 2 of the same new LED lights by the tailgate next, on one 3-way switch.

Assistance greatly appreciated!!

Jim

P.S. I know some people have had issues with the LED glowing when 'off' when making similar modifications, but I do not have this issue currently.

 

[Littleblackflash]

I'm not an expert on VW but I am on BMW systems which is similar.

The power for the lights comes from the BCM which will regulate the voltage to drive the lights at constant current (or could be voltage on VW). In you "on" position, you're not earthing back thought the BCM and therefore it can regulate the voltage and it seams to default to a low value. The battery voltage will vary and hence the brightness will vary because it can't regulate against anything. The idea of a BCM is to regulate the voltage so the interior lighting is a constant brightness and doesn't depend on battery voltage.

On you 3 way switch, connect the "on" position to the -BR neg wire and it should restore the brightness, similar to your "yet to be fitted" part,

I'm sure there will be a limit on the power available on the interior lighting, Most cars it's about 2Amps so you need to stay below this to ensure you still get full brightness.

 

[Jimm]

I'm not an expert on VW but I am on BMW systems which is similar.

The power for the lights comes from the BCM which will regulate the voltage to drive the lights at constant current (or could be voltage on VW). In you "on" position, you're not earthing back thought the BCM and therefore it can regulate the voltage and it seams to default to a low value. The battery voltage will vary and hence the brightness will vary because it can't regulate against anything. The idea of a BCM is to regulate the voltage so the interior lighting is a constant brightness and doesn't depend on battery voltage.

On you 3 way switch, connect the "on" position to the -BR neg wire and it should restore the brightness, similar to your "yet to be fitted" part,

I'm sure there will be a limit on the power available on the interior lighting, Most cars it's about 2Amps so you need to stay below this to ensure you still get full brightness.

Thanks for the reply. Ok so if I understand you right, it sounds like it initially, the battery was low, so when switched ‘on’, the BCM was unable to set the constant brightness, so it defaulted to very dim. I guess with switch in ‘door’ position, the BCM could also have limited the time the light was on, to limit power consumption whilst battery was low, hence only being on for 30 secs?

If this is the case, then this all makes sense! (But let me know if I’ve got the wrong end of the stick…..

Thanks again, much appreciated.