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If anyone is interested in saving $80 on installing fog lights using the OEM wiring harness, this is how I did it without buying a light stalk w/ fogs. The fog light functionality is not modified this way.

This is a moderately difficult install if you are unacquainted with electrical systems and trying to figure out how to do this on your own. A multimeter with diode functionality is essential.

I had already run wiring for my LED light bar, so the illumination on the fog switch was tied to the other switch. In all honesty, an illuminating switch is not preferable because of the way the switch is wired.

The plug to the stalks is shown in the FSM on page LT-46 as M28 on the bottom.



The BCM outputs 5V pulses on 5 output channels and measures those pulses on 5 input channels. BCS-3 shows how these signals are routed through the combination switches on the left and right stalks.



The computer knows which switches are on according to the pulse width and signal combinations measured on each input, shown on page LT-48 (no picture, not necessary for install).

In theory, the fog lamp signal is routed out of Output 5, through the fog light switch, through a diode, and into Input 4. Output 5 is pin 7 (Pink) on M28 and Input 4 is pin 11 (Grey).



The pin count is from the right upper corner in the above picture. 1 is the upper right corner (blank pin), 7 is the upper left, 8 is the lower right (blank pin) and 16 is the lower left.

Connector M28 connects to the back of the right stalk.



There is a small black 8 pin connector that the stalk seats into. This black connector connects to the left stalk, where the fog light switch is located.



At this point I was thrown a curve ball. With the stalks connected and the headlights on, I jumpered across pins 7 and 11 on M28 with a diode. The fog lights did not turn on. In fact, with everything off, these pins turned on the parking lights.

After some poking around, I identified pins 6 (sky blue) and 14 (orange) as the correct locations for the fog light switch. I did not want to rip my dash apart to check the pins at the BCM, so there may be some difference in the wire color and pin-out at the BCM that was not replicated at the stalk end of M28, but that is unlikely, as the wire colors match the pin locations. Either way, placing a diode across pins 6 and 14 with the headlights on would turn on the fog lights. They function exactly as they would with a stalk w/ fogs.



I used some splicing connectors on the M28 connector wires to bring them to the OTRATTW switch I purchased. I re-wrapped the OEM wiring and heatshrinked the new wires and routed them to the blank near my LED light bar switch.



The diode needs to be oriented so that the cathode (the end with a marking) is connected to pin 6 (sky blue)





Because the BCM does not provide 12 VDC on the ouptuts, the LED on the rocker switch will not illuminate when the switch is on. The lower LED is lit through my pre-existing wiring, and turns on with the parking lights. Because the fog lights are controlled by the computer, even if the switch is on (and light is on) the fogs may in fact still be off. Therefore, an illuminating switch is not particularly useful because it won't properly indicate the state of the fog lights.

 
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