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How To: Fog lights as DRLs on 986


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After reading the 987 DRL How To I figured I could recreate the concept on my 2004 986 so….

In use: with ignition on the front LED fog lights are on. If dipped headlight is on the fogs are off. If dipped headlight is on and the light switch is pulled (once or twice) the fogs are on.

Normal disclaimers: disconnect battery, I’m not responsible if you burn your fingers or worse your carpet mats, etc.

Purchased relay from here. The benefit is that the relay comes with a carrier so that, positioned conveniently, it can be removed leaving the carrier and wiring intact should Mr. Plod or Mr. MOT feel aggrieved at my ingenuity.

You’ll also need:

Soldering kit

Insulation tape

Scalpel or similar sharp implement (wife’s tongue will not cut it)

Wire cutters and strippers

T20 torx and small flat blade screwdriver to get access to rear of light switch.

The relay is NC (normally closed), in other words when the coil is not energised with 12V the switch contacts are closed. If I’m insulting your intelligence, get over it :whistle1: Thus supplying a fused ignition-on 12V to the pole of the switch and the NC contact of that switch to the fog light feed will have the fogs light up when the key is turned.

Supplying the relay coil with a ground and 12V from the headlight feed (post switch) will result in the coil energising when the headlights are on flipping the relay switch and turning the fogs off.

The relay used has the contacts and wiring below. The relay connections with their labels and the wire colours are identified – once again this was my relay, it may not be yours so double check! Most relays have a label / impression on the case stating the connections.

Appropriate wire colours also identified for the connections into the light switch loom.


Remove, with the wire cutters or strippers 5mm of the insulation from each of the relay wires and then tin with solder.

Disconnect battery and then get access to the back of the light switch. No point reinventing the wheel so follow the guide here. No need to remove the 24mm nut as the switch itself can stay in place.

Originally intended cutting the necessary wires and splicing in the relay connections giving the advantage that heat shrink would slide over them however, the loom was quite taught and so changed my mind and insulated with tape. May come back and revise this later if my OCD keeps me awake – it’s safe and that’s what counts.

Working on a single wire at a time use the scalpel to remove some of the insulation from the loom wire and tin it with solder (found it helped to use a plastic tool to hold the wire away from its friends whilst soldering). Be careful not to rest the soldering iron against the dash, your fingers or the neighbouring wires – don’t lay it down in the foot well on your mats either!


Solder in the appropriate relay wire making sure that it lies alongside the loom wire as if it is coming from the loom toward the switch. This removes stress from the solder joint when you tuck everything away as the relay wires will not have to immediately double back on themselves.

Check the joint for strength – tug on it – and if happy insulate it with tape then move on to the next wire.

When all four wires are soldered up and insulated connect the battery, push the switch knob on and give things a test – hopefully you’ll now find out now that you’re a genius. However, if things don’t operate as they should visually check everything but first check you plugged in the relay to the carrier if you have that setup.

If you still cannot get things working as they should post the symptom and I’ll try to help.

Add a cable tie to hold the relay wires alongside the loom for strength then tuck the relay through the dash and above the heater duct for easy access later then refit the dash assembly.




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  • 1 month later...

Good work Daz, any pics of how the car looks with just the fogs in their DR setting?


Me too please!

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  • 4 weeks later...
  • 3 years later...

Many thanks Sniktaw - just finished modifying my fog lights as DRL's as per your instructions - perfect!

I didn't solder the wires however - a bit radical - used compression cable connectors and although a bit of a fiddle, means I can remove them if necessary and only leave a small incision in the insulation. I used cable ties to secure the relay to the lighting harness to stop it flopping about and a potential disconnect. Ive also fitted LED's in place of the normal bulbs which just fit with a bit of fiddling.

Thanks again from a chilly Cape Town!

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  • 2 years later...

Hi Daz

I have just done this mod today, thank you for saving me a lot of head scratching. I had previously done this on my 993 but it was a lot easier on that car because you could just wire a different relay in.

Tks again


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