1998 Corolla Headlight problem

[john in texas]

I think I have a relay problem. Both daytime running lights work fine, unless I turn the headlight switch to "on", then both headlights turn off -- or if it's too dark outside, then both running lights turn off. If the car is on or off, using the headlight switch only turns off the running lights or doesn't turn on the headlights. If I use the headlights switch, all other lights come on, except the headlights. No other signal light problems observed. Any help appreciated. Thanks.