Keylight upgrade

[Stonejag 10]

I can't be the only one here who thinks the standard VW key light is absolutely useless. Not only is it a pain to get hold of the bulbs, they're incredibly dim and don't seem to last long before dying when they lose vacuum - at least in my pockets! So, I thought it was time for an upgrade. Simple enough if you know what you're doing :)

 

Here's the secret - I wanted to be able to put my key back to stock if I ever changed my mind, which means modifying the bulb. First I picked up a high-brightness 3mm LED from Maplin (didn't have any in the bits box) - I think it was part number UF74P for 64 pence. My bulb had already lost the seal between the glass and the metal base, so I removed the glass envelope and soldered the legs of the LED into the base - positive leg to the centre contact, negative to the case body. It's important to get it straight and cut the legs to the right length to keep the same overall 'bulb' length, otherwise it'll either protrude or not make good contact inside the key. Then I carefully snapped chunks of the glass away until just the crown remained (didn't have my Dremel to hand - cutting it would have been much easier, in retrospect!) and attached it over the top of the LED with some Araldite. Lots of trial-fitting will let you tune it until it's the same length of the original - this needs careful attention if it's going to look stock once modified.

 

Next up, it was time to turn my attention to the battery. 1.5V isn't really enough to run an LED, even a high-efficiency one - mine claimed a Vf of 2.5V @ 20mA, so I needed a higher battery voltage. Happily, lithium cells have around twice the terminal voltage of alkalines and run at a comfortable 3V, so I just needed one that would fit in the space left by the strangely-shaped LR9 cell in the stock key. A CR1620 fits the bill nicely, and clips snugly into the VW logo - £0.59 from eBay.

 

Although it clips in fine, the base contact is larger than that of the LR9 so you'll need to add a small piece of masking tape like this to make sure each terminal hits the right part of the battery. It'll work without it, but you may need to wiggle the VW logo slightly (oo-er) to get it to light up - not very OEM. Since it's not as thick as the original battery you'll need to press the button slightly further to make it light up but it's not really noticeable.

 

All ready to reassemble - just fit the modified 'bulb' as normal. You may need to rotate it slightly if you didn't manage to line the glass up perfectly with the LED, otherwise it will point in slightly the wrong way when reassembled and look strange! I added a tiny extra blob of solder to the side of the metal part so I would always get a good contact.

 

Put back together again. Very close to OEM.

 

Except it isn't! :D

 

There are two reasons I went with a red LED - they're more efficient than other colours of LED, so they'll be brighter and the battery will last longer. Also red light affects your night-vision less than other colours of light so it's less dazzling and you'll be ready for night driving faster. White LEDs need 3.5V so won't light up as brightly, but if I can be bothered I might experiment with different colours if I stumble across a source of cheap donor bulbs in future :)

 

Worth doing? If you ever use the key light, definitely! Nice and bright now, like it always should have been really :)

 

Stone

[tony_ack 0]

key...light?

[lauraJ 0]

So this is what that button does?! amazing! Talking my other half into doing this.

[moneypit23 0]

Got all the bits to do this sitting on my desk at work so i might use a green one to match the interior lights, sad i know.

[Stonejag 10]

Green will be a bit disappointing - the semiconductor they're made of doesn't convert electricity to light as efficiently, so they need more current to get the same brightness as a red one. Since you're running it voltage-limited rather than current-limited they'll never be as bright as red ones - that's one of the reasons I used one :)

 

To give you an idea, here's a side-by-side comparison using a bigger lithium cell: (excuse the shoddy photo, phone camera)

 

The red one is so bright it saturates the camera sensor so it appears white and gives everything around it a red halo. By contrast the green one is just green! High-efficiency ones are a bit better but not by much. Next time around I might try stacking two lithium cells and using a white LED for extra oomph, will need some currrent-limiting to stop it blowing up though! :)

 

Stone

[fla 9]

good idea, thanks for sharing.

[Stonejag 10]

It's been brought to my attention that not everyone has a key with a light in :) No matter:

 

VagCat link

 

Getting part number 1H0837219A from the dealership will sort you out - give them your chassis number and they'll cut and code it for you. A website said it was £17.68 +vat but might be out of date :) An unmodified bulb is N 90314501.

 

Stone

[moneypit23 0]

Blue?

[Stonejag 10]

Blue would be the same as white, except slightly brighter - 'white LEDs' are just blue ones with a yellow phosphor in the lens so the mixture of light looks white-ish. I haven't got any lying around but I can give it a go next time I pass Maplin :)

[James. 7]

I only had mine apart the other day and thought of moving up to LED. Got a couple of free periods tomorrow, so that's my morning stitched up nicely. Cheers