i have a 1990 bronco last night i turned on the light's all came on except the headlight's.could someone please help on what to do to get the headlight's working again

I assume that you have already check the lamps and they're good. There a a couple issues that will cause them not to work. First, check the relay under the hood. You can swap in the relay from the A/C (they're the same) to see if the relay is bad. Next, check the switch plug/socket. They have a tenancy to melt. If it looks good the dimmer/switch may be bad. Remove the switch. It will look like the one in the picture (switch housing/plug color may vary ie. black, gray brown, white). To remove it, you will need to pull off the headlight and wiper knobs. Pull with an increasing force until they pop off. Its tough but they will come off. Then screws that hold the fuse cover in place. There should be 2. Now you can pop off the dash cover piece around the light and wiper switches. Now you have access to the switch mount hardware. If you know how to use a DVM, let me know and I can talk you through troubleshooting the switch but if you check around, you should be able to find the replacement switch for around 20 bucks. Good luck and let me know how it goes.