Replaced the headlight assemblies, worked for a week, now the lights wont work at all. Good fuses and relay. Thoughts?

Do the high beams work? How about he signal lights? seems to me a light relay (fuse) is gonzo. Basically, there is a light switch that is wired to a fuse/relay. From this fuse relay there is another wire that goes towards the headlights. Seeing both lights are not working chances are the fuse /relay is done for. Cheap and easy fix.

Test for voltage going into and out of the hi/low switch. If you have voltage at the headlights, check the ground wires.

Its a German car and they are known for electrical problems. Your problem lies within the Drivers light assembly, check the voltage voming into the headlight socket with multimeter and see if there are any voltage spikes or drops, alternating.

For the low beam problem, Swap relays 45 & 46 in the underhood fuse panel. Relay 46 is for the Low Beams. If that fixes the light, replace the relay that cam out of position 46.
Since the high mounted brake light is working, that indicates that the brake switch is good. You need to check the bulbs in the rear tail light assembly, if they are good, check fuse #34.

i think that car has a headlight relay if it does the relay is bad replace relay (relay should be in fuse box) if relay is good or doesn't have one headlight switch is bad or u have a short

reason head lights still work but won't start is cause the headlights don't require as much power to run as the starter does

First thing to do, is checking your fuse, then if fuse are ok, then check the relay, located under the hood by swtiching around with another relay of correct relay specs. If it works, then replace your relay, if not, check that relay if it works with another relay spot such as windows, and test the windows. If it is not the relay, then it could be your headlight lamps that is bad, check your rear tail lights to see if it comes on when you turn your headlights on, If the tail lights come on, then it is a good possibilty with the headlamps since the sorento are known to blow through head light bulb light crazy. I mean crazy. So maybe replace one side see if that would work, to really know for sure it's a headlight issue.

I would say try replacing headlight switch...I have the same problem and will be doing that tomorrow

the grounds may be bad they are behind headlamps but more than likely it is the switch

At first 1994 C280 high beams began to not connect regularly when stick pushed forward, then not at all. Drove high beams by pulling and holding stick back towards steering wheel until that stopped working, too. Shop said the turn signal switch was at fault-- had seen it many times before with W202; about $160 to replace. Haven't done it yet, but should be an easy fix?

 I’m inclined to believe you have a headlight switch problem and here’s why. There are 2 fuses one for each of the headlights on the vehicle. For the daytime running lights (DRL) to operate the fuse and wiring to the right head light has to be good, because it supplies the power for both headlights in the DRL mode. The fuse and wiring for the left headlight has to be good because the DRL relay needs power from that fuse to operate. The DRL relay in turn provides a path through the left headlight and wiring to ground. When you pull back on the dimmer switch, you are activating the flash to pass circuit of the headlight switch assembly. Because the flash to pass mode works you then know that the high beam wiring and headlight bulbs are in good condition. This also tells you that the ground circuit for the headlight switch is good. In many newer vehicles, the headlight switch doesn't provide power to the lights. The headlight switch has now become the path to ground to complete the circuit. The headlight switch and the high/low beam dimmer control are one assembly so when you replace one you get the other free. Such a deal! My coffee bet is on the headlight switch assembly.