I’ve heard and read many different ways to go about this, to start off, I have a 99 s70 that did not have fog lights, however all the wiring is there. These are LED fog lights as well. So far I have a switch hooked up (not a Volvo fog light switch) and have added a J relay to the relay panel under the steering wheel. The relay box under the hood has a grey case lighting control relay. Now the confusion starts! The switch I have has 3 prongs (prong 1 is power, prong 2 is accessory, prong 3 is ground). As for the plug on the car there are 4 wires, green/orange, pink, pink/brown, and black. First question is, is the pink wire bringing power to one fog light and the pink/brown wire to the other fog light? Or is the pink/brown wire also a ground wire? Question 2, I’ve heard that I’ll need a green case lighting control relay and a “213 jumper” relay. Are those necessary?
I can post pictures as well if any are needed!
there are also some weird things happening. With the green/orange wire on prong 1 and black wire on prong 3, connecting just the pink wire to prong 2 (with car off) flicking the switch turns the radio on and off. When putting just the pink/brown wire on prong 2 there is a faint buzzing sound coming from somewhere on the fuse/relay panel under the steering wheel. Any way I connect the pink and pink/brown wires the fog lights still will not turn on.

 

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According to my wiring diagram..... The black wire is ground for the switch. The pink wire comes from the instrument cluster rheostat to control the brightness of the switch background light at night. The Green/Orange wire comes from pin 87 on the fog light relay and provides 12V power to the orange "on" indicator in the factory fog light switch, and 12V power to the fog lights themselves. Lastly, the brown/pink wire. When the factory switch is off, the brown/pink wire is open. When the factory switch is on, the ground from the black wire is connected to the brown/pink wire, which sends a ground to the fog light relay on pin 85, causing the relay to close and sending 12v power out pin 87 to the lights, turning them on. Hope that helps. I think your best bet is to get a factory fog light switch and hook it up that way.

Good luck