Odd behaviour of map-reading lights
 

A recent thread (about dimming mirrors) asked if the D2 (facelift presumably) and D3 interior mirrors were the same, which prompted me to look at mine as I wondered if both types have map lights and/or anything else in them.

I noticed that the nearside map light was on and offside off, and neither changed when operating the switches. Turning the exterior lights on did switch on the little red downlighters in the unit.

This was in daylight, I decided to check later after dark. By then both map lights were on, though not that brightly; again the switches did nothing.

I decided to start the car and everything immediately returned to normal, the map lights at full brightness and switches operating normally.

All my interior lighting is LED now, so they probably wouldn't need anything like the full 12v to light up, but I do wonder what can have been going on; any thoughts anyone? :Confused:

Just checked mine (non-LED) and they behave as expected: The switches turn them on and off, except when the rest of the interior lighting is on.

Sounds like a small amount of current is getting through to your LEDs when they should be off, possibly from a sensing circuit (alarm maybe?) that's using a pull-up resistor.

I've seen it happen in A6s C5 where the LED interior lights makes all the lights act odd.

Put incandescent bulbs back in and they work as normal.

No idea what it would be that causes it in in the LEDs unless its back to the resistance value of the LEDs being different.

Have this phenomenon in HGVs all the time, especially where newer trailers fitted with LED lighting is connected to older tractor units from a pre LED era.

You can be standing in the yard at night and the indicators on a trailer will be 'glowing' gently on one side.

Tractor unit is shut off completely but the leds still glow

I've asked various auto electrical people about it over the years but never managed to get a consistent answer!

I think it's a "glitch" inside the interior lighting circuits/controller probably "enhanced" by a faulty/failing LED bulb.

I noticed again today that the drivers side map bulb was on again, dimly.
I suspect that has a fault and is doing something to the electronics.

Just opening a door turns on the map lights along with the interior lights so I'd guess that's done by "earthing" one side and that the other is always live (+12v). The separate switch will probably do the same.

It seems likely that the interior light circuitry "earths" those bulbs to a lesser extent all the time for some reason at present.
I'm going to replace the bulb that is currently dim and see if that sorts it out. They're just a bit of a PITA to get at. :tuttut:

Edit: Just having another look it's actually intermittent, so maybe the bulb isn't seated properly.

Top tip from someone (cant remember who...might have been Oli) on here years ago was to use thin nose pliers with insulating tape wrapped around them to remove and replace these bulbs, works a treat+++

Its sometime more difficult getting LED lamps in/out there than getting the old filament lamps out due to (often) greater size. It helps if you are an amateur but enthusiastic gynaecologist +++

Can't recall what they are, possibly the bayonet type with offset pins?

The originals are 5W W5W filaments and therefore are the push-fit type +++ Should be easier to get out but they did require some force IIRC.

I've just been and given them a "wiggle" to make sure the contacts are good; felt secure enough already though. Fine at present anyway. :Confused: