S197 Fog Light Operation Modification
In this article we will modify the wiring harness to allow the S197 Fog Lights to run with High Beam Headlights running Under normal operation the Fog Lights operation is as follows:
1. Running lamps ON and Fog Lights ON.
2. Running Lamps ON with Low Beam Headlights ON and Fog Lights ON.
3.Running Lamps ON with High Beam Headlights ON Fog lights do not operate.
This I am told is because in some states it is illegal to run your Fog Lights with the High Beam Headlights on. Check your local Inspection criteria to verify if this applies to you.
Also this mod will disable the Auto Turn Off of the Fog Lights.
With the Normal configuration it presents us with a few problems.
1. If you wanted to convert your Fog Lights to Driving Lights you would not be able to run your Driving Lights with your High Beam Headlights.
This would negate the advantage of being able to put more light in front of you which is why you would convert to Driving Lights in the first place.
2. In the case that you did not convert your Fog Lights but desired to have
more light directly in front of your vehicle while your High Beam lights were
ON you would not have this option.
So just how do you convert you’re lights to operate as you desire?
We set out to figure this out.
First we consulted the factory wiring diagrams and found they were rather lacking in the completeness of the diagrams themselves. We ran a few scab wires to experiment with the operation. And also tested at various points with our Volt Ohm meter. In the end what we discovered was the following.
When the High Beam Headlights (HB) were turned ON the ground for the Fog Light Relay (FLR) would eliminated. The in turn would de-energize the FLR and drop the power off to the Fog Lights. This is done in the Smart Junction Box (SJB) somehow. Also we found that just adding a dedicated ground to the FLR would cause the Fog Lights to be ON at all times. Key ON or Key OFF. So that was not an option obviously.
So how can we add our option to our system?
1. Install a dedicated switch for our Fog Lights and run a new harness.
2. Figure out a way to Fool the SJB into thinking the ground was interrupted even though it was not.
3. Modify the SJB to allow our option.
We wanted to use the existing wiring and switch. So how do we fool the SJB or how do we bypass it?
And this is how we did it:
This is what you will need:
1. Roll of Electrical Tape.
2. Appx 6 foot Length of wire 22 gauge or slightly larger.
3. Assorted Splices.
4. Roll of plastic conduit (Optional).
1. Disconnect your Battery.
2. The SJB is located on the passenger side of the car under the kick panel.
Smart Junction Box
3. There is a Blue plug that contains an Orange with Light Green stripe
(OR/LG) wire in it. This is the wire that comes from our Fog Light Switch
into the SJB to complete our FLR ground when the switch is in the ON
Orange Light Green Wire at SJB
4. We will need to Cut this wire and splice our new bypass wire to the side going to the switch. Use a butt splice as we did. This wire Must Be CUT and the wire going to the plug dead ended. If you do not this causes your radio to go crazy. I do not know why but it does.
Splice at SJB
5. The other end of our bypass wire will be at the Bussed Electrical Center (BEC) on the passenger side of our Engine compartment.
6. First run your wire from the passenger compartment into the Engine compartment. We did this by slightly pulling the grommet around the orange cable that goes into the engine compartment, and running our new wire through it. It will enter the Engine compartment under the battery tray. Then route the wire to your BEC. We then replaced the grommet in place. It is soft and easily can be pushed back into place.
New wire ran into Engine Compartment
7. Next we wanted a clean setup so we opted to use a wire conduit to protect the new wire and give us a clean setup so we ran a conduit over our new wire to the firewall.
Conduit with New wire routing
New Wire with Conduit installed at BEC
8. After our wire and conduit were in place and routed we need to tap into our DB/W wire.
9. At the BEC we will need to tap into a Dark Blue with White Stripe (DB/W) wire located in the second from the front harness going into the BEC. We will use a splice here again, or you can use a wire tap (Scotch Lock). You must splice your new wire to the wire going into the BEC or just tap into it with a wire tap. Tap into the wire using your wire taps or splices as you choose.
Dark Blue White wire at BEC
Dark Blue/White wire at BEC
10. Then reconnect your battery and give it a try.
11. If all went well your Fog lights should work with your HB Lights ON using your existing factory switch.
Fog Lights with High Beams ON
12. Just re-tape your conduits and put your previously disturbed areas back together and your done!!!
Now we got to find some replacement Driving Lights!