Recently the front fog lights stopped working on my S70. The rear fogs work fine. I do have after stock fog lights but the car did originally come with sock front and rear fog lights. I tried looking at the yellow fog lamp switch, I was getting 11.xx volts to the switch. I will double check the terminals, but I was also getting one of the terminals to toggle on off 11.xx volts by switching so I think the switch is good along with the fuse. I am not getting power to the gray fog light pigtail nor I am getting the dash light to turn on when I turn on the switch.

Could this be the relay? If so which one?

 

What year is the car?

 

Okay, looking at my wiring diagram, power to the fog lights comes from battery, through the high beam switch and then to the main headlight relay. from there it goes through the fog light relay, to the switch, and then to the lights. My suggestion is to test the fog light switch first to eliminate it, then start tracing power back to where it is lost. I'm betting a bad fog light relay, especially if the headlights and highbeams function properly. The relays should be under the fuse box in the engine bay. Remove the torx screws and take the top of the fuse box cover off and the relays are underneath. Good luck and post back if you run into issues.

 

The car is a 1998 S70. I will double check the switch but believe it to be working. I will document the pin numbers this time for reference along with a photo..

 

I attached a copy of the wiring diagram for a 1995 850. I have used this for troubleshooting our 1998 S70 as they are 95% the same car. Most of the time even the wire colors are the same. Look at page 24 of the pdf for the fog light diagram.

 

Thanks for sharing. I will take a look and post what I find!

 

The fog relay on a 98 is hanging under the cowl fuse box. I don't know if you've ever looked up under the dash under the fuse box, but there is a little army of relays up in there. It's apparently on the upper left corner of that assembly.

The lamps themselves are brittle and the bulbs may have lost contact just for that reason. That's the only problem I've ever had with mine. There is a fuse in the fusebox for fog lamps. This powers the contact side of the fog relay.

The wiring involved is pretty disturbingly complicated, I'd say, on the 98 wiring diagram. The front fog relay receives control power from the headlight relay, and is ground switched through the fog lamp switch on the dash. The diagram shows that Euro/USA/Japan cars are all different in respect of how the fog relay control power comes off the headlight relay. I imagine the rules are different about when you are allowed to have fogs on, and the USA/CDN version the fogs are only on when you have headlights on with low beams.

One helpful diagnostic tool (if the LED worked) is that one bulb in the switch is powered off the fog lamp relay. So if that light came on, it would eliminate 95% of the wiring diagram from being the problem. If you've never seen that light come on, then that wouldn't mean much.

Here is the 98 diagram for comparison. The symbology on these is pretty hard; 2/1 is the headlight relay and that is not shown here. 2/2 is the fog lamp relay. 3/99 is front fog light switch. Anything 31 is ground. The 23 (8 slice pizza) is a junction. 10/5 and 10/6 are the actual lamps that aren't working.

 

Comparing the two diagrams, it looks like the 850 is identical except for the "bridge" but much more clear. I think a 98 doesn't have the bridge. Don't hold me to that. Those were cute, a jumper wire in a little relay box. Don't know what that was for. Maybe outside the USA it wasn't a bridge, I don't know.

 

Good call on the light in the switch.......Definitely eliminates a lot of potential trouble if it is working.