all lights work as designed with the exception of the high beam. when switching from low to high beam the headlights go off- no lo or hi beams, but the high beam indicator comes on. when switching back to low beam the headlights come back on. No fuses are blown, but am not sure if this is controlled by a relay. any help would be appreciated.

 

I would start by checking the bulbs and the connectors for the headlight wiring... Something could be loose

 

Like bone says check the bulbs first. Did this happen all at once or are you new to this car? I had to replace the dimmer/ turn signal/headlight switch in my 02 L series, in my opinion they are pretty light duty parts.

 

+1 both bulbs may be burned out (if they are separate bulbs) or the contacts inside the connectors have developed corrosion and are no longer making contact. Cannot always tell the filament is gone;

If HALOGEN bulbs, do NOT touch with bare fingers --use gloves. Use a multimeter and check for Resistance--if good, pretty close to 0, if bad, open circuit.

I have actually had two different brake light bulbs work as running lights but fail to light w the brake pedal depressed. In both cases, one of the contacts of this 2 filament bulb was corroded inside the bulb socket, preventing the current from passing through the second filament.

If you find corrosion on the connectors at the base of the socket, pull the fuse for the hi beams, then scrape the corrosion off so that clean metal can be seen. (If you leave the fuse in and slip, you'll short the connectors to ground and blow the fuse). If the bulbs are badly corroded just replace them (HALOGENS no touch!). Put the fuse back in and measure for V betw center contact and ground. If V is present reinsert bulbs and all should be fine