Leo stared at the tangled mess of wires spilling out of a 1990s drift car. He had just swapped in a modern, high-performance engine, but the factory wiring harness looked like a bowl of colorful spaghetti. To make the car run, he needed to perform a —essentially "re-mapping" the physical connections between the engine’s sensors and the new Engine Control Unit (ECU). Step 1: The Blueprint
"Repack" is industry jargon for transplanting the internal logic board of an ECU into a different mechanical housing. Why do this?
Before installing the ECU in the car, check for shorts between power and ground on the bench. Plug it in. Turn the key to "ON" (do not start). Smell for burning electronics. Listen for the fuel pump prime. If you see smoke, you reversed the main power and ground.