Hank Themak

Have 1996 Chevy Cheyenne K3500 with 350 engine. Problem: No headlights which were working fine and just stopped working. Checked and replaced fuze and one sealed beam but still not working. Just not getting power to both sealed beams. Hi-Lo dimmer switch works as dash indicator light does work. Wiring diagram shows a diode that is located in the under hood fuze bock. Do they fail? Wiring diagram also shows a couple of relays but can't locate them under the hood. Not located in the under hood fuze and relay block. Where are they located. What else should I check?