QX4: How to modify fog lights to DRLs

OVERVIEW:

The factory design uses a separate relay for the fog lights. The fog light relay coil circuit is in series with the headlamp circuit with the fog lamp switch being located after the relay. By simply replacing the relay’s headlight power source with another ignition-based power source, we can achieve the desired behavior.

PURPOSE:
Performing this modification will change the behavior of the fog light switch. The factory design allows the fog lights to operate only when the low beams are on. The fog lights will now operate any time the ignition is on.

BACKGROUND:
Prior to this modification, the headlights only worked when the low beams were on.  Additionally, the fog lamps turned off when the high beams were activated. I drive with my headlights on during the days and wanted to be able to use my fog lights as daytime running lights. In order to do accomplish these goals, the lights would need to be wired in such a way that the fog lights would turn on any time the fog light switch was turned on regardless of the headlight status. In addition, the lights would need to turn off whenever the ignition was turned off.

DISCLAIMER:
This guide outlines the procedure I used to modify my 1999 QX4. I do not know what other years this modificaton would apply to. This mod may be illegal in some areas, please check local laws. Perform these modifications AT YOUR OWN RISK.  I am not responsible if your lights go out in the middle of the night.

PROCEDURE:
STEP 1-
Located the relay box under the hood. Mine was on the driver’s side fender. Identify the relay for the fog lamps using the guide on top. Mine was identified as “FR FOG”.  Remove the cover to expose the relays.

STEP 2-

Remove the factory relay. I chose to preserve the factory relay and replace it with a relay from Radio Shack, part number #275-0226. You will need to trim the mounting tab from the relay in order for it to fit in the relay box. Locate the pin on the relay labeled “85” and remove it completely.

STEP 3-
Remove the cover from the relay by prying it off with a small screwdriver.

STEP 4-

Identify the post inside the relay that corresponds to pin 85. Solder a wire to the post. Be sure that you have a good connection. I used brown wire since this is a common color for a wire that is active only when the ignition is on. Drill a hole or cut a small groove in the relay cover and thread the wire through it.

STEP 5-

Connect the brown wire to the new power supply source. I connected mine to the A/C relay in the relay box. I again replaced the relay with the same Radio Shack relay.  Make the connection by soldering the wire to pin 30 and making a hole in the relay cover like you did in step 4. Do not remove any of the pins on the A/C relay. Replace the relays and test operation of the fog lamps and A/C.

If all goes well, you shall have independently functioning fog lights!

Originally posted by bmlawless