Dim Headlight

I have a dim headlamp in my 1997 toyota corolla. I replaced the bulb, but it's still dim. I measured the voltage across the bulb and it is less than 5V. The other bulb is fine, and the battery is holding over 12V under these conditions. Obviously, the 7 or so volts is being dropped somewhere else in the system. I don't have a wiring diagram handy. Any ideas where to look for the problem?

Thanks in advance!