Where is the modulator valve located on a 1985 Chevy C10 truck?

The 1985 Chevy C10's modulator valve isn't located in one single, easily identifiable spot like a standalone component. It's actually integrated into the transmission itself. More specifically, it's part of the transmission's valve body. You won't find it as a separate part you can just pull off. To access it, you would need to remove the transmission.