Adding Fog lights to the Brake lights
First pull down the knee bolster so you can have clear access to the Bulb Failure Relay harness.
Unplug Connector from back of Foglight switch and run it down past the Bolster with the Bulb Failure Relay. See PICs
On Bulb Failure Relay there is a Blue wire with a Red trace, connector number 54S.
This is the wire that comes from the Brake Switch. You need to strip back some of the insulation to connect the Anode of the Diode to. See PIC
Connector from Fog lights has two wires going to it. A white with blue trace and a Solid White wire.
The Solid White goes to the Fog lights, that is the one that needs to be Cut. Cut this with enough wire on both sides so that you can attach additional wires to it.
The Anode side of the second diode attaches to the Cut solid white wire that now just goes to the Connector of the Fog light switch.
The Cathode of this second diode goes with the Cathode of the first diode to the Cut Solid White wire that goes to the fog lights (not the side that goes to the Switch).
In the PIC below I have a Dual diode. This means that there are two anodes (the outside wires) that internally go to a single Cathode. It makes the wiring simpler.
Small description of what’s going on:
The Anode side of the diode that attaches to the Blue/red
wire (of the car’s harness), you do not cut,
you just strip the insulation back a bit and solder the Anode to
it. It is ONLY the White wire from the
Fog light switch that gets cut.
Diodes act like 'One way' Valves. Looking at the electronic symbol of Diode you can see it looks like an arrow showing the direction the 'valve’ will allow electricity to flow.
So what I am doing is taking power from the Brake pedal (Blue /red wire) and adding a ‘valve’ so it can flow to the Foglights (White wire). But because it is a One way valve, When you Turn on the Foglight switch, the electricity cannot flow to the Brakelights. There is an issue… when you step on the brakes, the little light on the Foglight switch will light up because we just added power that circuit. To stop that from happening, we add the second diode. Basically putting a one way valve in between the foglight switch and the foglights. That’s why we have to cut the white wire to do this.
The diode in the picture is a Dual Diode. there are two diodes in that one 'Block' see the diagram on the right side of the schematic (BELOW) Click here to open schematic pdf in new window