Dave,
Couple of other things to check. Locate the low beam terminal (TB1-4?) in the electrical bay under the driver's window. Verify you have 12V on that terminal when low beam is selected. If not, probably the dimmer switch or relay. If 12v is present, the problem is between the TB1-4 and the lights. I'd look for a bad connection/crimp. Be sure to also verify that the connections on TB 1-4 are tight.
Good luck! Steve