I've searched quite a bit on this and other forums and have gleaned some info on the topic, but nothing seems to be exactly what I'm experiencing. My driver's side headlight went out a few weeks ago along with the "bulb failure" dash message.

At first I thought it was the bulb, but a replacement bulb didn't do the trick. Thus began the troubleshooting. I have 12V at the fuse location, and the fuse is good. I then checked the bulb plug, the one that literally plugs into the bulb, and it's dead at 0V. I then unplugged the main harness. Pic attached. Finding about 12 different slots/locations and not sure which was which or which should show 12V, I unplugged the passenger side and just started putting the voltmeter's leads on different locations until I found that if I put the negative lead on #9, I got 12V at pins 2 & 3. On the driver's side, I then found that #2 has 12V but #3 is dead, not at 0V exactly but at 0.65V. So, it seems #3 is for the low beam that's not working. I assume #2 supplies power to the high beam, which btw works fine. It's only the low beam on the driver's side that's out. Passenger side is fine.

I read a bit about the shunt but if I read reliable info about it, if there shunt were bad then both sides would be affected. Is that right?

So...I'm at an impasse. Is it just the harness that's bad? And if so, which one? The main one, the pigtail that plugs into the bulb, or both? For full disclosure, I run modified H9's for low beams bc the stockers are so pathetic. I'm hoping this issue isn't related to running the higher 65W bulbs. I also use H9's in my Prius and well as in my dad's Traverse with no issues, and in general this mod doesn't seem to lead to wires melting or issues, based on what I've read. None of the wires or connectors I've seen look melted or burnt.

Any ideas?

 

you need to get the electrical schematic for your car, figure out how to read the thing, then track the power from the ECM to the bulb. I have a Ford made connector as it looks like you are showing, so none of the colors of wires are correct with the schematic. but if you work hard enough you can cross reference each contact to the correct color.

My problem was different, a previous repair had actually been done incorrectly so it took me forever to figure it out. somebody mixed a ground wire with a positive wire.

 

Not sure what model/year you have but in many 2000+ year Volvos the low beams are relayed vie the CEM (central electronic module). Its a common point of failure due to blown relays and cold solder joints (ie solder that cracks over time leading to bad connections between the relays and CEM board). Do a quick search on CEM for your model to see where its located (I think for V70s its above the passenger side footwell - its on the drivers side for my S40). Also if you need a schematic, check out volvowiringdiagrams.com (really)