I'm trying to chase down a pesky pair of non-op amber side markers on 08 XJ358. The fuse controls other lights that work fine, so not a fuse issue. Both markers have working bulbs, no power at either socket. Tracing the power wire back, looking for a common failure point, I discovered a male plug with 3 wires just behind the left fog light. Wire colors are: black with yellow (same as marker lights) red with purple, and yellow with red. Wondering if anyone has taken off the bumper cover and noticed same? Or noticed same plugged into something which I haven't noticed or found.

Alternatively, anyone with a late-model wiring diagram that suggests a point at which the front marker light pair hits a larger connector of some sort that I could test with a meter would be amusing to see.

 

I am not sure about an x358, but on the x350 it depends on to which ‘marker’ lights you are referring. Fore of the front wheels are the blinkers/indicators and aft of the wheels are marker lights.

Maybe you are expecting the blinkers to act as markers? I only suggest this based on the proximity to the connector behind the left fog light that you were referencing. If this is the case, try your emergency flashers and see if they illuminate these lights. Again, this may be different on the x358, as i don’t remember the function of all the lights on these models.
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On my X350, the turn flasher was indeed part of the side spear, but on the 358 it's on the tip of the outside mirror. The side only has markers, red in back, amber in front, both on the bumper cover ends.
My next try will be to remove the plastic tray underside from the bumper cover when I get it on the lift next week. That will allow a more thorough look-around, and perhaps clues to the mystery plug. Perhaps at least a chance to put a meter on the contacts looking for 12 volts.