Disabling DRL at Switch on 99-05 VW Jetta
MK4 Jettas leave the factory with a bi-halogen (dual-filament) headlight bulb. Since the car has only one main beam, and the the daytime running lights run off those same bulbs, you need to disable the DRLs to install HIDs. The reason being, that the DRL runs the light at 80% power and that will destroy HID ballasts rather quickly.
There is an easy way to do this that simply involves bending a pin down in the connector of the headlight switch. The pin will be labeled TFL and will be in different locations depending on whether you have a US-spec or European-spec headlight switch.
Step 1: Remove the Headlight Switch
To remove the headlight switch you push the dial in, and turn it clockwise like you are turning on the lights. Once you can’t push it any further, you pull it out towards you.
Step 2: Unplug the Headlight Switch
Put your fingers at opposite sides and wiggle the plug side-to-side until it comes out. There is no trick here, it just comes out by wiggling it free.
Step 3: Locate the TFL Pin
On either switch the TFL pin is the 3rd one from the edge; depending on how you flipped it, this can vary. The thing to note, is that the pin is labeled “TFL” no matter which switch you have.
Step 4: Bend TFL Pin Flat
Now use a flat screwdriver to just flatten the pin so it looks like the picture in step 3.
Step 5: Plug it Back In
Plug the switch back in and verify that it works. If your dash lights didn’t come back on when you plugged it back in, it’s either not plugged back in all the way, or it’s upside-down.
If your dash lights came back on and all the turn signals and everything appear to work, then with the headlight switch in the off position; lower the parking brake if it’s engaged, and if the headlights don’t come on, you are golden. Now you may go ahead and hook up your HID relay without damaging your ballasts or bulbs.