It looks like the dimmer switch, part of the MFS is your bad guy. The exact same output from the headlamp switch is used for both headlamp modes, switched from circuit to circuit by the dimmer switch, so if the hi-beams are OK... power and ground to the headlamps are also OK.
Check your violet/ white wire out of the MFS for power when switched to dims. If it's not present, investigate the MFS connector for damage to the connector pins or switch. Hi-beams come out the red/ orange wire, by the way...
No CTM is used in this year, saving you a little mental grief! It's a hard-wire situation, either the low-beam filaments in both bulbs are out or you're not getting power to the bulbs. My info shows no fused circuits after the dimmer switch, so it's just a matter of getting power from the dimmer switch to the headlamps, most likely the MFS itself.
Remember... the violet/ white wire should show power at the MFS when switched to lo-beams. If not, you're gonna need a switch.
Nope. So sorry to have missed those points, rench!
Since you can have the headlamps turned off and still get the optical horn function, there had to be a separate feed to the dimmer switch. It still comes via the headlamp switch feed, but is an internal output of the switch after the built-in headlamp breaker.
The headlamp switch must have a power source for the optical horn to work, so your fuse to the switch is OK. Output on either L2 circuit (light green) is questionable and needs to be checked. If you DO get a strong output on L2, the problem will be something after the headlamp switch, probably the MFS. Just keep following it.
Thanks for setting me straight!