BMW e30 Writeup: Replacing OBC backlight with LEDs

[Doigal]

Whilst this is being done on an aussie spec e30 318i (m40), it should apply to all non M3 e30s. Just be sure to check before plunging into it! Also, this is a right hand drive car, so any references to driver or passenger side need to be reversed for US and europe. Any prices are in AUD.

Usual legal crap - I'm not a pro and have no pretentions to be one. If your doing this for yourself, just be sure to go and buy a bentley and read that first. For reading pleasure only, dont try it at home!

Never Replace OBC lights again!

The idea for this mod came from here:
http://newling.no-ip.com/rep/bordcom...led_licht.html

When I was in preperation for retrofitting an OBC into my car, both of the ones I ended up with had dead light bars. It seems even if you are lucky enough to get one that has a light bar intact, its best to replace it before it goes in. Its just not easy to get to once its in the car. Replacement ones are available from dealers for about US$30 (or so I hear), or any small pair of 6 volt globes. I prefered to go for 2 small LEDs, as the car is more likly to be dead of rust before they die.

LEDsales sells wide angle amber (VERY close to the stock lights colour) LEDs for about 20c each. The only problem is that they have a $10 order minimum, but as I had to stock up on a whole bunch of stuff this wasnt a problem. Any good electronics store should have something simular. You'll also need a resistor.

To work out what resistor, you need to do some simple maths. Assuming that it runs at 14v, and the two LEDs take up 4v each, the resistor needs to get rid of the remaining 6v. LEDs generally like to be run at about 20mA, so using V=IR, we get a 300 ohm resistor for running at 20mA. I didnt have any 300 ohm ones, but I had a big pile of 240ohm, so I just made do with that. 25mA is generally not going to kill them.

So, once you've got the two leds and the resistor, its time to wire it up. You need to remove the light bar from the OBC (that part isnt covered here). Once its removed, gently remove the PCB from the plastic casing.





Now, desolder the old bulbs. Its easiest if you mark the circuit board like this for the next step.



Now, you need to solder the anode (longer leg) in the hole that has positive sign near it. Dont put the other leg through the hole, but bend it up out of the way for the resistor. The cathode (shorter leg) of the other LED goes into the hole with the minus sign. Again, same thing with the other leg.



Now you need to solder in the resistor. This needs to be done as close as possible to the center of the PCB. Mine is a little bit off in this picture, and needed to be given a little 'encouragement' to fit back into the case.



Now, pop the case back on and if you have access to a 12v supply now would be a good time to test it out.



And the final result:



There you go! For about 43c australian, you'll never have to replace your OBC backlight again. Once the OBC itself is out this only takes about 5~10 minutes as well. Quick and easy!

[Tom]

genius!

[Doigal]

Thanks tom!

After reading though some other threads, this isnt e30 specific, and would work for any cars with that type of backlight.

[Dan@dms]

Well done!

One question, where where you when you did this considering it was -30

[Doigal]

One question, where where you when you did this considering it was -30

Melbournes a little colder these days!

[dans_325]

i did this a couple months back but replaced it with original bulbs i sourced off ebay in the US. only cost me a few dollars but i was happy considering bmw wanted $150 for the white bit of plastic with a basic pcb and 2 bulbs! maybe my mech exagerated the price as he was the one who called for me but i wasn't going to shell out more than i had to for a bulb or two! i know now you can buy the part from BMA for $30US + shipping.
not that that matters!! love your solution!