Where is the Hummer h2 left headlight relay?

Hummer h2 left headlight relay must be in the control cabinet or control box. It is difficult to point out in detail without a circuit diagram. You can find the real thing according to the relay characteristics provided below.

As an electrical control device, relay is connected in the circuit to form two control systems: control system (also called input loop) and controlled system (also called output loop). You can look along the circuit. Relays generally have several main contacts, plus two coil contacts, similar to contactors. The main contact is connected to the controlled system, and the coil contact is connected to the control system, but the relay can usually see the contacts. You should be able to find them according to this feature.