Check your fuses...there are usually seperate fuses for right and left headlights (for safety - so if the fuse blows it won't knock both lights out). I would bet a nickel you've just got a blown or broken fuse. Clean up the contacts before replacing it. Here's the electrical service data for your car, look at Page 10:
http://skinnerbox.steaky.org/Service/W123/w123CD2/Program/ETM/82_240.pdf
Check Fuse #13, it is only for the LH low beam!
Here's the complete service manual set:
http://skinnerbox.steaky.org/Service/W123/Index/616index.html