How to wire the fog light relay circuit to the parking lights or as an independent circuit.

(This tip was written for XJ models up to '91.  I have not been able to confirm the wire colors for
later models yet, but the concept is the same and will still provide a good guideline for all model years.)

    The following may seem confusing as you read it, but it is way easier that it sounds.  Once you are looking at the wires, it all becomes clear.

    You will need to gain access to the back of the fog light switch and the head light switch.  This is easier if you remove the dash bezel.  Just four screws, two at the top of the main instrument opening, one over the headlight sw, and one over the lighter, (you might have to remove the stereo face from some after market stereo units) and it pulls out.

    At the back of the Fog SW, there are three wires:  black, light green w/ black stripe, and light green.  Locate the light green wire (violet w/ white after '91), this is the power lead from the dimmer switch that is activated with the low beams.  You will want to follow it back far enough to cut it (and securely tape off the end form the dimmer switch) and route it to the back of the headlight switch. (Unless you want to wire the fog light circuit to the high beam circuit, then skip the next paragraph).

    Now at the back of the headlight SW, look for the terminal with two dark blue wires attached (after '91 a red stripe was added).  These are the wires to the parking and instrument lights.  You will want to "tap" into one of these (doesn't matter which, you are only powering a low current relay). Use a "blue" crimp-on wiretap to make your connection to one of the dark blue wires.  Now if you couldn't get enough of the light green wire from the fog SW, to reach the dark blue wire, you can merely splice on another short piece of similar wire so it will reach the tap, but I think you have the basic idea of what needs to be done.

    If you want to wire the fog circuit for driving lights, so they come on with the high beams, then follow the light green wire (from the fog light sw) to the point where it joins the wire loom that comes out of the steering column.  There will be many wires here, you are looking for the two white wires(*).  One is for the high beam indicator light and goes to the back of the instrument cluster, the other is the wire that goes out to the high beams.  Either wire is okay to tap into (whichever one is easier to access).  Cut the light green wire at a point where you can use a "blue" crimp-on wiretap to make your connection to one of the white wires.  Be sure you use the end coming from the fog light switch, and securely tape the end from the steering column.  After you have confirmed proper operation of the headlights, and fog light circuit, you're ready to put everything back together.

(*) Some models have three white wires. If so, the third is for the brake light circuit, but it changes color to green somewhere between the hazard switch, and the point where the wires exit the column.  On some models it happens inside the column, others just after it leaves, so if you see three white wires, you can either use the one that goes to the instrument cluster, or confirm which wire changes to green, and avoid that one.  Also after '91 the high beam wires are red w/ orange stripe.

    If you want to wire the fog switch to work independently of the lights altogether, instead of wiring it to the dark Blue wires, you can run it to any 12v source.  Many models have a spare positions for add on circuits in the fuse box that will accept a standard male spade push-in connector.  They are usually marked "BAT", (hot all the time), or "ACC" or "IGN". These positions are not fused, so you will need to use an inline fuse holder (5 amp is plenty).  Some even have "Spare" fuse positions that have no fuse installed but have a hot (or switched) side, that you can push a male connector into (again using your own fuse).  If yours has any one of these, you're in luck.  Just crimp on a male connector to your wire to the fog light switch and plug it in.

    The next easiest way is to use a fuse tap (a small brass clip that fastens to one leg of the fuse, and provides a male spade to  attach a standard female spade connector to).  These work fairly well but make fuse replacement a little more difficult.  You won't have to add a fuse if you use this method, just be sure you are on the load side of the fuse and not the supply (hot) side.  This can be determined with a meter or a test-light, by removing the fuse and verifying which side of the fuse socket is hot... if you put your tap on the side that is hot, the circuit you are adding will not be fused.  Relays are measured in milliamps, so you won't really be overloading the existing circuit by using it's fuse.  Depending on how you want your lights to operate (always hot or switched with the key), you can use the test-light to find a suitable fuse to tap into.

    Finally, you can always take a fused lead and run it to the main electrical junction on the Starter Relay (early models) or the Power Distribution Box (later models), both are located just behind the battery, and are hot all the time, so be sure to disconnect your battery before working on this terminal.