Help 86 Sierra Classic no headlights!

[drhchevy]

Hi all, I need some advice. My 86 Sierra has park lights, tailights, signals and brake lights but no headlights, high or low. I changed the switch with a used one, nothing. There is power going to the headlight switch and all the fusible links from the starter are showing power at the fuseblock or firewall. The 5 amp accessory fuse is good and has power going to it on both sides of the fuse. I also disconnected the lighting harness from the fuseblock and when I jump it it from the battery, the light will come on. I also cleaned all the grounds that I saw related to the lights. I am at a total loss here and traced the Chilton schematics to no avail as well. Any help would be much appreciated. Thank you very much

[Wrenchbender Ret]

Check your dimmer switch.