ECU controls the Engine matey. It does this by using sensors all over the engine and the drivetrain.

Your dash clocks will also use these sensors. For example your temp gauge is on the engine, your RPM will take its information from the coil pack or the ECU. Your Speedo will either be a mechanical drive cable from the Gearbox or an electrical sensor in the gearbox.

On a car your age then headlights and indicators are very simple relay driven switched circuits. On more modern cars with CAN bus ECU systems and automatic functions then these can often be integrated into the ECU