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Foglight switch rewire

Article by: Chris Paschall


For the ones that are having the dreaded headlight shutting down,melting headlight switch,and no fog light at all!!!

There is a very easy way to fix this problem!!!

First you will need some parts:

1)  A Bosch 30-40amp relay (5-pole)
2)  About 3 feet of red 10-12gauge wire
3)  10 speaker terminals 10 and 18  gauge (local electrical shop,or stereo shop)
4)  Also 18 gauge wire two or three different colors (black,yellow,grey)
5)  One 10-12 gauge fuse holder (ato style)
6)  One 30 amp fuse  (ato style plastic blade type  green)
7)  Solder and soldering gun
8)  Screw driver (small flat blade)
9)  8mm socket or 5/16" socket and ratchet
10)  18 gauge butt connectors(3 or 4), and one 10 gauge butt connector
11)  two or three 18 gauge ring terminal and self tapping screws
12)  Volt meter or 12V test light


First remove the head light switch, this is easily done by taking a small flat screwdriver, and with slight pressure on the switch(outward)  push locking tabs on the left side of switch then the switch should just slide out at this point.

Note the colors of the wires on the small two pin plug, should be a 18 gauge light blue with black trace, and a 14gauge light brown with orange trace.

Ok now remove lower dash cover(under steering column) by removing the three  8mm bolts underneath the cover.  After bolts are removed lightly pull cover straight outward toward the seat back.CAUTION  do not pull straight up or down , or you will break all the mounting clips off and can not be repaired.

Now locate the 10 gauge yellow  wire at the ignition switch harness, verify this is a constant power source with a test light, or volt meter.  Now strip about a 1/2 inch of the insulation off of this wire to expose the copper wrappings.  Now take the 10 gauge fuse holder and strip about 1inch of of this, and wrap this wire around the exposed yellow wire tightly and solder and tape well, connect 10 gauge red wire to fuse holder with butt connector.

Now take the black 18 gauge wire and put a ring terminal on it and connect to a good ground (preferably a metal surface)

Run these wires up to the location of the head light switch.

Now remember those colors we talked about earlier,  now take the light blue with black trace wire and cut it and connect the side that goes from the switch to the dark brown wire of the headlight switch plug.

Now take the light brown with orange and cut it.  Connect the 18 gauge grey wire to the side going to the switch, then connect the yellow 18 gauge to the other side of the light brown /orange wire. 

Now you should have 4 wires up by the headlight switch compartment.  10 gauge red, 18 gauge black, 18 gauge grey, 18 gauge yellow

Take the relay now   NOTE  that there are numbers and letters on the bottom of it

should be   85, 86, 87, 87a, 30

Put the speaker terminal (female spade) on all of the wires at this point, make sure to make all the wires the same length, this will make the install a lot cleaner.

Now after this has been done  take the 10 gauge red wire and connect it to terminal 30 on the relay.

Take the yellow 18 gauge and connect it to terminal 87 of the relay

Take the 18 gauge grey wire and connect it to terminal 86 of the relay

Take the 18 gauge black wire and connect it to terminal 85 of relay

Terminal 87a will not be used in this application

Wrap relay and harness with tape to protect

Tuck relay and harness neatly behind headlight switch and reinstall switch assembly.

Insert 30 amp fuse and test,  if all is ok proceed to put car back together at this point.

NOTE:  with this setup you will be able to run your fog lights with only the parking light on!!!   Now That's COOL!!!



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