[Ron in Quincy]

If you installed new headlight wiring harnesses, some of those available have large connectors and will short across bringing on both high and low beams. If this is not the problem then check the terminal block in the light switch to be sure it is terminated properly. Generally the wires to the headlights are: Red with tracer= high beam, Green with tracer= low beam, Yellow with tracer= Parking light.

Ron