I have a 92 sc4000 and my right Lo Beam went out the other day and when I replaced it, it immediately burnt out. I am assuming it is a short as the fuses seem to be ok.
What can I do to know for sure that this is the problem? Or, should I just bring it to a shop and let them deal with it...thanks.

 

my right side lowbeam burned out too. what I found was a short in the bulb harness itself. Look in the slots where the bulb plugs in it might look burned like mine. I have been looking to get it replaced but everybody i talk to says i have to buy a complete new wiring harness for it. Junkyards that do have parts wont sell just the plastic part ethier and want too much for the whole harness. if this turns out to be your problem let me know if you get it fixed and how.

 

If your headlight worked right after you replaced it, the wiring is probably good. You may have accidently touched the bulb with your finger when you replaced it. The oil from your skin stays on the glass of the bulb. The heat from the bulb somehow burns the oil residue causing the bulb to fail very quickly. Look at the new (not working) bulb and see if the tiny wires inside are broken. This happened to me once...

 

brutus is right, oil from your fingers can get on the glass of bulb, if you touch it. The bulb gets so hot that is boils the oil from your finger tips causing the bulb have a very short life span. IF you do touch the glass be accident, use rubbing alchoal to clean it and then light it air dry.