LED DRL issue despite fitting 50w 6ohm resistors?

Zac

Registered User
Would really appreciate some help here. I fitted PS19W LED bulbs in the sidelights/DRL to MY10 headlights. Look great.

Lights will stay on with the engine off. However, after a couple of minutes of driving they're both completely out and not working. The resistors are wired in parallel, anchored to the chassis and heat up so they're working.
So I'm assuming it's flagging up as a blown bulb and shutting off the supply...but I don't understand why with 6 ohm resistors. Can you use too little resistance?!

Car is 2004 TDI with full MY10 exterior. No DIS and no error wanting light on the dash, the bulbs just won't stay on! So annoying!

Any help would be really appreciated, have been up until the early hours trying to resolve this. Thanks
 

Murton

Member
VCDS Map User
With 6 ohm resistors you will be drawing 24W through them plug whatever the LED DRLs are taking. The car is expecting to only supply 19W.

I would measure the current through the LED DRLs and then get the correct resistors to increase the power up to 19W
 

Zac

Registered User
Thanks for the help. So I guess the car is shutting the supply off due to the excessive power? My multimeter has given up the ghost so I'm going in blind.

Just used a couple of online calculators for Ohm's and power laws; for a 19w bulb I need to emulate a current of 1.58 amps, of which I require a resistance of 7.6 ohms.

Assuming negligible current through the LED (~25mA), I'm going to try a 10ohm/15w resistor tomorrow and see if I finally have success.

Thanks again.
 

Zac

Registered User
Arghhhhh!

So I tried various combinations of resistors to no avail.

I also tried wiring the original 19w halogen bulbs back in parallel... interestingly the halogens remained lit when the led bulbs turned off. Does this mean that the only explanation is that I have duff LEDs? Only caveat to that is I can't understand why they stay on before I turn on the engine.

If somebody could resolve this I would be eternally grateful!
 

Murton

Member
VCDS Map User
If the bulbs in parallel are on but the LEDs arn't then it can only really be the LEDs that are at fault.

On my car I have the older headlights with normally a P21W DRL bulb. I bought LED DRLs from trups and then used VCDS to recode the car to tell it that it had LED DRLs. This changed the way they operated and stopped errors but now when the main headlights are on the DRLs are automatically dimmed.
Maybe yours do the same and the lower voltage when dimmed is causing the LEDs to shut off.
 

Granta

Registered User
I fitted a pair of CREE led DRLs from trups tonight to a facelift TDi and they work perfectly. No coding required and built in resistors. If I was you i would get a pair as he has a good reputation round the forum and now wiring in resistors needed!
 

Zac

Registered User
Interesting resolution with the VCDS. Unfortunately I don't have that luxury :(

For anybody with similar problems in future... I put the original bulbs back into their harness and wired the LEDs in parallel...this worked, whereas putting the LED in the harness and the halogens in parallel didn't (??).

Worked out the resistance for the original 5w bulbs at 28ohms. So the control unit is still programmed for that, and not the facelifted 19w bulbs. So if you're fitting LED sidelights to a facelifted 8P with the new H16 bulb, then consider that the control unit still wants the 5w bulb which you require 28ohms of resistance for.

My car is very sensitive as I tried various combinations of resistors from 6 to 25ohms; had to be 28ohms or the LEDs wouldn't stay on, confirmed this by wiring 3 resistors (2x 10ohm, 1 x 8ohm) in series on one side. 28ohm/50w resistors now on the way and hopefully a permanent solution!

Thank you all for taking the time to reply.
 
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