How I made my auto headlight switch pass the new MOT

[audifan]

The auto headlight switch as we all know does not come with a functioning tel tale for the rear fogs. This is now a mot failure ( yes some testers either know the switch cannot be accidentally left on rear fogs or do not check either way a gamble. I tried to find a way to use the existing LED that is used only to indicate the switch is in programming mode but failed. So this is what I did.
I removed the auto switch and its sensor from the car to take it apart. On the rear ( on my switch ) there were 2 small screws holding the wiring part to the mechanical part of the switch.
I took these 2 screws out and slowly and carefully pulled them apart. This left the internals of the mechanical switch exposed.The other half had the board for the illumination and tell tales.
The switch half has long channels the light passes through from the leds to the fascia icons with plenty of space for another led. Great news.
I already bought prewired 12v 3mm green led as front fogs illuminate in green although amber is the more common colour. The led was sourced from Amazon ( pack of 20 ) and looked how to wire it in.
The first issue was how to get the wires from the mechanical half to the electrical half as no obvious path for the wires could be seen, so I cut a 3mm square out of the switch on the edge next to where the rear fog tell tale would be fitted. The led was placed in the long channel for the rear fog and the wires passed through the newly cut slot in the casing.
The 2 halves of the switch were carefully reassembled and the 2 screws refitted.
The wiring was run externally along the body of the switch and passed into the connectors block through a small hole which was used for the light sensor on my switch.
Now to wire the leads into the pins on the switch. The red led wire was secured with a small blob of solder to the NSL pin on the switch and the black wire again soldered on this time to pin 31. These 2 pins are opposite on the diagonal as you look at the switch.
The switch was temporarily reconnected to the car loom to test it. I now have an auto switch that does everything and now has a working tell tale for the rear fog.
Did not take any picture of the dismantling or wiring only the finished result.

Switch refitted

Ignition on

Side lights on, notice the rear fog illumination not as good due to the led blocking part of it

The front and rear fogs on

Front fogs only on

Better shot showing less bright rear fog icon.

 

[audifan]

Just to add after driving the car at night the rear for icon is about 50% the brightness of the other icons when illuminated. If I wanted to I could move the new led to the side as there is space and glue it there so more switch illumination could reach the icon.

 

[audifan]

Here are 3 night shots

This shows the icon illumination for rear fog not as bright due to led blocking original led.

This one shows front fog on and that you can see the less bright rear fog icon.

Both front and rear fogs on. Extra green is reflection off the chrome on the switch.

 

[A2 Louis]

Here are 3 night shots
View attachment 50410
This shows the icon illumination for rear fog not as bright due to led blocking original led.
View attachment 50411
This one shows front fog on and that you can see the less bright rear fog icon.
View attachment 50412
Both front and rear fogs on. Extra green is reflection off the chrome on the switch.

Where did you buy the auto headlight switch from if you don’t mind me asking or is it of a AUDI TT MK2 ? ?

 

[audifan]

@A2 Louis bought from ebay switch came from China. No it is not a TT switch it is for a VW Golf MK4 etc. Similar to this one
Chrome-AUTO-Headlight-Switch-Light-Sensor-Module-For-VW-Golf-Mk4-Passat-Polo-

See also my thread on fitting the chrome ring

Chrome bezel ring for auto headlights conversion

I fitted an auto headlight switch designed for a golf mk4 bought off ebay. I decided that i wanted to use the new switch as is and set about measuring the external diameter. I transferred this dimension onto the a2 faceplate then used a dremel to cut most of the material away and finished off...

www.a2oc.net

 

[audifan]

Just make sure you buy one that includes the wired light sensor and has the big plug on the rear as there are ones without the sensor and also ones with the small wiring plug neither are suitable for the A2.

 

[Alan_uk]

On the rear ( on my switch ) there were 2 small screws holding the wiring part to the mechanical part of the switch.

Hi. Do you recall what those screws were? I've a pack of small hex, torx, security hex, philips, slotted & pozi but none fit. The smallest is marked 3mm. My eyes are straining to see what the screws are but they appear to be hex.

Took over 10 photos and this is the best I can do.

 

[audifan]

To be honest not sure now but do think they are torx, may have been an odd size and had to use my phone tool torx. Have a good look with a light and magnifying glass either hex or torx. They were not very tight as they are only into plastic so you may be able to use a fine flat blade to get them out. Sorry not much help .It will be the weekend before I can pull mine to check.

 

[audifan]

@Alan_uk Just been having a think, now pretty sure the 2 screws are 1.5mm HEX.

 

[Alan_uk]

Thanks. Used a 1.4mm flat bladed screwdriver pressing down hard whilst turning. Quite hard to get leverage but once it moves then easy. They are 10mm long.

Next problem was that the 2 halves did not easily part. Turned out that one of the sprung locating lugs had a lug recessed behind it

I pressed down with a c4mm screwdriver. Once opened I could see 2 LEDs where the rear fogs are, which surprised me. Tomorrow I will test to see if the second (lower) one lights or not.

Note the plunger. At first it seems that it needs retracting to fit the 2 halves together. If it is depressed then it is just possible to hold it with ones nail at point X. However, by having the switch at the off (0) position the 2 halves do seem to go back together without the need to depress the plunger.

It appears that as the switch is pull out for the fogs, then the plunger is depressed in 2 stages and operates 2 contacts for front and rear fogs.

to be continued...

 

[audifan]

That is correct. Yes there are 2 leds already on the board, unfortunately when they designed the auto lights the lower rear fog light only flashes to indicate switch programming and never illuminates for the rear fogs, unless you have a later version.

 

[Alan_uk]

Here's some photos. As the LEDs blinded the camera, I've added some red/green circles. As stated earlier the plunger operates the fog switches.

1. Headlights On. Note that to the right of the green LED at 1 p'clock you can see the hidden lug referred to earlier.

2. Front Fogs On, plunger 1/2 depressed

2. Read Fogs On, plunger fully depressed

As Audifan says, the lower LED (bottom left) is not on and only flashes when programming. Also as Audifan pointed out earlier, the Red Rear Fog remains on meaning any additional LED will complete with this LED.

I've yet to find out what the LED at the very top, to the right of the Auto LED, is for. So far it has remained off. May be it comes on to change Auto from red to green when it is trigger by low light and auto switches on the lights.

 

[Alan_uk]

I looked at the 12v LEDs with resistor used by audifan but the ones I saw looked too big and the resistor was right next to the LED making it inflexible. I then recalled I had these yellow fairy light string for some long forgotten project:

and decided to cut off the end one and use that. On ebay look for Fairy String Lights Yellow Battery Operated

As yellow LEDs operate around 2v and typically need to consume 20mA (with a max of 30mA) I needed to add a suitable resistor. I used this online ohms calculator. Alternators typically generate 13.8v to 14.4v and we need to subtract the 2v for the LED to get the voltage drop across the resistor, i.e. 11.8v to 12.4v. The calculators says the resistor needs to be 690ohms to 720ohms. The nearest resistor I had was 680ohms and feeding this back into the calculator gives a current of 20.29mA at 11.8v and 21.18ma at 12.4v. Perfect.

The wires seem to be coated in thin plastic but I decided to cover them in shrink wrap wide enough to go over the resistor. First I needed to determine the positive and negative leads. I used the resistor and a 9V PP9 battery and then cut the positive lead shorter.

Once soldered and tested with a PP9 battery I heated the shrink wrap using a metal shield with an aperture to protect the LED and unwrapped wires.

With a razor saw I cut 2 slots next to the Rear Fogs LED at point C on the photo below. But the slots were too fine and I opened them up with a miniature hack saw. I also carefully cut slots into the edge of the printed circuit board, having determined there was no circuit on the underside.

The LED was secured with a drop of superglue in the slots in the black plastic but not at the printed circuit board. The LED was tested with a 9v PP9 battery. The wires were secured with a glue gun at various points. [the white line is referenced below]

I agree with audifan that it is not practical to open up the whole unit and solder inside to the back of the pins. But instead to solder to the foot of the pins inside the socket. There is already a spare hole into the socket on the opposite side to the hole where the sensor cable goes in. However, I decided not to use that as my cables would then have to go down the side of the unit and I felt there was not enough clearance at points X, see photo:

Instead inside the socket I noticed a gap where there were no pins and decided to drill a hole there. The white line above marks were there is a faint line in the housing that is the position of the back of the socket.

The wires were first tinned and then soldered as described by audifan. The 2 pins where cleaned with a glass fibre pencil. The wires were held in place for soldering with BluTack I had a shaky hand day, got solder some too far up a pin, and then had to used braided wire to remove the solder, and ended up melting some of the plastic. Maybe covering the tops of the pins with masking tape might of helped. So this next photo is touched up!

The red and black wires were given a touch of superglue near their soldered connections in case they come loose. One needs to use thin wire (it's only handling 20mA) as the plug is meant to go right to the back of the socket and any wires will inhibit that. It is possible that the plug lugs may not engage but the plug does grip well anyway.

Finally I tested it and it was OK. The Rear Fogs is not a pure yellow as the yellow LED mixes with the red LED that does not go out, to make orange. But I confident that it will get through the MOT. By using a small yellow LED the red LED is not blocked and therefore not dimmed.

In the photos below I had to manipulate the reds as my camera shows them as orange!

Just Front Fogs On .......................................... and with Rear Fogs On:

Thanks to audifan for showing this mod is possible.

 

[audifan]

If anyone is interested these are the green LED I fitted.

 

[audifan]

As a footnote to this, the current Auto switches with Bluetooth do now have the built in tell tale lamp so these instructions do not apply to the latest switches.

 

[DuncanA2]

As a footnote to this, the current Auto switches with Bluetooth do now have the built in tell tale lamp so these instructions do not apply to the latest switches.

Hi there,

I still have the "old style" lightswitch with the seperate box connecting to the car wiringloom.
I think your solution should work as well for my situation, however most of the links to your pictures are lost or broken. Is there a way I /we can retrieve those? I'm specifically interested in the wiring part and the adaptation of the lightswitch casing.

Hope you can help.

Cheers Duncan

 

[audifan]

@DuncanA2 , I call your version of the switch the MK1, my one the MK2 and the bluetooth the MK3.

Let me know exactly what you want and I'll do my best to help out. Also does the actual light switch have the big plug or does it have the small plug?

Send me a PM would be the easiest method.

 

[DuncanA2]

Alright, I have the Mk1 version. The lightswitch has the small connector between the switch and electronics-box which in turn is connected to the wiringloom of the car. The electronics bits I thonk I can manage, but I am curious how you did the wiring bit to the needed led.

Thanks in advance.