I’ve been attempting to install front fog lights on my XJS, but ran into a shortage of the factory switch packs necessary to have the “plug & play” experience.
In order to keep everything as original as possible, I’ve found a way to patch into the rear fog light switch that I’ll describe below.

First, thanks to everyone here and all the threads I’ve found that were necessary to illuminate the way to my solution.
Special thanks to (xjsv12) for posting a wiring diagram that was extremely helpful.

The Plan:

The very simple version of the relay modification.

Because there is existing wiring, fusing, and a relay for the front fog lamps even if the option is not installed, the hard part is already done. There is no running new wires through the bodywork.
There are two modifications to be made to the existing harnesses, marked below on the diagram.



The more detailed & helpful version.

Modification #1 is to change the 85 pin (Black/Red wire) into a Ground. There’s a convenient grounding point just ahead of the air filter housing that I used, you’ll see a pic soon.
Modification #2 is to splice the 86 pin (Red/Orange wire) into the Rear Fog Light Relay control (Yellow Solid wire). This is done at the loom connector behind the dashboard.



Front Fog Light Relay. Engine compartment, Left side, third back from the front.



The ground point I used for the new 85 pin ground. The temporary setup is shown with the relay on four extensions for convenience.

Once you’re done running the new ground wire to the relay harness (this DOES involve cutting & splicing-please use heat-shrink and other weather proofing) and have everything tucked away neatly, you’re done under the bonnet!

Moving inside:

*Carefully* remove the switch pack (Demist/Fog Light) and the clock from the dash.
These are tension-clipped in, I used a very thin-bladed flathead screwdriver with a bit of painters tape folded over the tip to prevent scratching the veneer.



If you disconnect the wire loom from the switch pack, you can pull it out through the clock cutout for more working space.

Obviously I did that, then reconnected it because I’d forgotten to document with pics. You can see our targeted wire (Front Fog relay-Red/Orange) partially extracted from the loom in the background.



Detail view of the back of the Demist/Fog Light wire loom. We’re going to splice the Red/Orange into the Yellow Solid.

Doing that will provide control of the Front Fog relay along with the Rear Fog relay from the single factory switch.



Rather ugly, but it’s spliced and shrink-wrapped under the tape.

At this point, all your modifications are done, carefully tuck away the wires & looms, get everything back into it’s place and give it a test.
You should see what’s in the next picture.



Because we’ve used the factory wiring, the proper indicators illuminate along with the fog lights. Ignore the other indicators, I didn’t have the engine running as I was in the garage with the door closed.

And that’s it. Now all that’s left is to choose, purchase and mount your preferred fog lights. (As close to original style as possible, in my opinion.)
I have a set of Hella 550 ambers that I temporarily wired in just to make sure everything worked, I’ll be permanently mounting them once I’ve built and painted the mounting plates.

Hopefully this will help someone out there.

Cheers!

 

Great job!

Thank you for posting.

 

Very useful to some I’m sure and well written. Well done.

 

Got a pic of the lights? I was thinking of mounting a set ala IrocZ

 

As close as i could get to the mounting plates. Unfortunately i forgot to take a picture before I installed them.

These are what I went with, as you can see in the third picture they have a completely different mounting style than the factory type.

The lights are Hella 550 Comet-Amber from Summit Racing. They were the closest in size/make that I found without going original.
I used a pair of 1 x 2.5 x .25 inch steel plates to mount them, mostly because I had some of it already in the garage.

The machine screws mount to the threaded factory holes in the bumper. The screws are (if I remember correctly-I’ve tossed the receipt) M6x20mm stainless with lock washers that I bought at Home Depot.
I had to replace the factory wiring plugs, but weatherproof M/F plug kits are easy to source.

 

They do have a quality appearance in the lenses. Thanks

 

The lenses are decently heavy glass, and they come with heavy rubber/plastic covers that snap on over the lights.

You’re very welcome!

 

HELP, HELP! I have original Hella lights on my '93 that driver-side glass is busted. Found an OEM Hella light cover, but not even Hella distributor in AZ has a replacement light. The size is specific to the fit the OEM cover. Any sources????

Thx for all the great threads and info over the years here!
Dave in AZ

 

I think I remember those lenses being permanently attached to the lamp housing.
After having to replace two cracked lenses I dumped the fog lights altogether.

 

Am I missing something? When you switch on the front fogs the backs come on at the same time?

 

That’s correct, mostly.

In this setup, you’re using the existing rear fog light switch and power source to activate the front fog light relay.

In practice, it will cause both the front fog lights & the rear to illuminate when you press the single (rear) fog light switch as opposed to the factory setup, which had separate front and rear switches.