He grabbed his multimeter and a long, sharp probe. He went back to the truck. The ECU was located behind the glove box, a black box with three large multi-colored plugs. He didn't need to remove it; he needed to back-probe the wires while the ignition was on.

*Disclaimer: The story above is illustrative. ECU pinouts are highly specific to the vehicle's serial number and

He followed the harness from the engine bay into the cabin. Near the firewall, tucked behind a mess of aftermarket alarm wires installed by a previous owner, he saw it. A spliced wire, crudely twisted together with electrical tape that had lost its adhesive.

The following images illustrate the 4HL1 control systems and ECU hardware typical for these engines:

For professional-grade data, Jaltest provides technical data on ECU configurations, software versions, and fault code memory management for Isuzu N-Series/Elf trucks.