1978 firebird no headlights

I don't have any headlights I replaced the dimmer switch,and checked the fusible link.I have parking lights and when I checked the plug at he dimmer and there is no power at the blue wire and when I put 12 volts to the other 2 wires I have lights. Does anyone have any ideas where this problem might be.

By dimmer switch, you mean High Beam, Low Beam switch?

yes the hi beam low beam switch on the floor.