On a 1994 Chevy truck, the Electronic Spark Control (ESC) module isn't a separate, easily identifiable unit like an ECM. The ESC function is integrated *within* the Powertrain Control Module (PCM), also sometimes called the Engine Control Module (ECM). Therefore, you won't find a separate ESC module; it's part of the larger PCM.
The PCM's location varies slightly depending on the specific model of your 1994 Chevy truck (C1500, K1500, etc.), but it's typically found under the hood, often attached to the firewall or near the driver's side fender. It's usually a fairly large rectangular box with numerous connectors.
