Before you go much farther, why don't you just replace all the 4 bulbs with new ones. Try that. A seemingly good bulb can be the cause. Plus, its real easy.

I used to teach troubleshooting on complex systems. Try easy things first. Also, try to fix just one side, not both. If its a common problem, it will show up. Lots of folks like to look for commonalities. If you have two problems, you'll be working a long time.

So, neither headlight works, must be something common, eh? No, after spending time checking switch and dimmer, turns out both bulbs bad. A long time ago, but I learned from that.

I didn't own a meter at the time, and that didn't help. These days, they give them away at Harbor Freight.


Good luck.