Driver's side low-beam headlight out

Solution: If both headlights aren't working, it's unlikely that a bulb is at fault. The likely cause is a fuse, headlight relay, headlight switch, dimmer switch or a wiring fault. ... Consult your owner's manual to locate the main fuse for the headlight circuit and replace that fuse with one having the same amp rating.
OR
Most total headlight failures are caused by a bad component like a fuse, relay, or module. Wiring problems can also cause both headlights to stop working. High beam headlights don't work or low beams don't work. The cause: A burned out bulb, or a problem with the high beam switch or relay.
https://www.lifewire.com/fix-non-working-headlights-4137021

Find the hot and take it to the bulb

check the circuit for a low beam relay that is not working

there should have a fuse layout or description in the fuse compartment near or under the light switch.

Replace the headlight bulb.

Under the hood, there are two round head lamp covers on each side. One for high beam and one for low beams. The low beam is the outer cover. Turn this cover counter clockwise and remove. This will expose the back of the bulb. There is a small clip holding the bulb into the headlight housing, but you must unplug the light before removing clip. Once you have unplugged the light, the small metal clip can now be undone. on the side opposite the hinge, push the clip in towards the casing and then to one side (which way to push depends on which light it is.) Then the clip will release. you can now remove the bulb. place new bulb in and make sure it securely fits into position. reinstall the clip and reconnect the power. check for propeer function of the lamp before replaceing the cover. Once you confirm lamp is working replace cover and you are done.

This is easiest to see on the passanger side light. The driver side is slightly more cramped.

Look for the left headlight relay to be at fault.

H13 HALOGEN HEADLIGHT BULB, SOLD INDIVIDUALLY -- Low 55/high 65-watt halogen bulb; 12.8 volts; P26.4t base; A high quality, direct fit OE replacement headlight bulb




How to Replace a Headlight Bulb
(DIY Complexity: Easy / Time: 0.9 hour)

Parts:
1. Headlight Bulb

Tools:
1. Screwdriver
2. 1/4 in. Drive Ratchet
3. Socket Set

Steps:
Step 1 Open the hood and locate the headlight assembly.
o Tip: Most headlight assemblies have a place in the rear to gain access to the headlight bulb.
o Tip: It is recommended that headlight bulbs are replaced in pairs.
o Tip: Always make sure the struts on the hood can fully support the weight of the hood so that it does not close on you while working. The use of a hood prop can securely hold it in place.
o Tip: Safety Tip:Always wear safety glasses when working on your vehicle. Wear other personal protective equipment (PPE) when necessary, for example latex gloves or safety shoes.

Step 2 Gain access to headlight bulb.
o Tip: It is a good idea to check the high beam and low beam headlight bulbs at this time.

Step 3 Disconnect the wiring harness and replace the old headlight bulb with a new one.

Step 4 Turn on the headlights and check high and low beams to verify repairs.

Hope this help (remember rated this help). Good luck.

The adjustment screws/nuts should be located either on the top of the headlamp assembly, behind the headlamp assembly, or near the frame rail by the radiator support.

You will have vertical adjustment screws for each independent beam (separate highs and separate lows, but will be same screw if highs and lows are the same bulb). You may also have additional horizontal adjustment screws as well

Park your car on a level ground 30 feet from a wall and measure the height from the ground to the bulb and mark on a wall (do this for highs beams and low beams if the bulbs are separate, if highs and lows are the same bulb, only do it for the lows)

For Low Beams: If the headlights read VOR, then aim the brightest part or cutoff part just below the mark on the wall. If it says VOL or nothing, aim them 2 inches below the mark on the wall.

For High Beams (if separate from low beams): Aim the headlight directly at the line you marked on the wall.

how do you change left low beam bulb on 2003 mercedes e320