Where is the glow plug relay on a 1988 ford f250 7.3L diesel?

The glow plug relay on a 1988 Ford F250 7.3L diesel is located under the hood, on the driver's side of the engine compartment. It is a black, rectangular box with a red wire attached to it. The glow plug relay is responsible for providing power to the glow plugs, which heat up the combustion chambers of the engine before starting it.