Hi-Beam is Out

[VetteVet]

Here is a diagram showing the wiring. The tan and green wires come through the firewall block from the dimmer switch and run to the left headlight plug. They join the wires to the right headlight plug there and run over to the right headlight.

When you turn on the headlight switch you should get power to the dimmer switch via a 12 gauge blue wire, and it switches power to the tan or green wire. Green is high beam and tan is low beam. You must have power to the left headlight so your problem is between the left headlight and the right headlight.
You can see in the diagram that the tan and green wire run from the left light over to the right. The tan wire is the low beam wire and it must be OK because you say the high beam doesn't work. That means the ground is good and either the high beam filament is burned out or the green wire or the plug is bad.

If you don't have the correct wiring then you will have to trace it through the harness.

Check the diagram.