I got into my '04 Discovery to drive home tonight, and the headlights wouldn't turn on. I initially thought maybe a fuse had just gone, but as soon as I saw that there are separate fuses for the left and right lights, I knew that wasn't it. I replaced them anyway, but it didn't resurrect my low beams. The high beams still work, so I had to drive home with them. Good thing my headlight lenses are super oxidized. When I got home and parked, there was a fairly loud buzzing/humming noise coming from under the hood up by the firewall. It was definitely in the engine compartment, not the passenger compartment. I popped the hood and started to look around, but it stopped. I don't recall hearing this noise before.

What's going on that took out both of my headlights even though they're seemingly on different circuits? Is my stalk bad? How could that account for the buzzing?

 

I think there is a relay somewhere for the low beams. I would check that. I remember one time I heard a weird buzzing coming near the firewall and it was my Idle air control valve vibrating. I have no idea why or if it is normal, but it only happened twice.

 

I can't find a relay for low beams. I see two relays for the turn signals, but they're working fine. Would it be possible to test for current across the low beam fuses to see if they're getting power? I have a multi-meter, but not the expertise to use it to its full potential.

*Edit* I do see relays for the daytime running lights. If one of them has failed, could it prevent the switch from turning on the low beams, or are they separate bulbs?

 

It was the bulbs. It was the bulbs, everyone! You can all go home now...