See Figure 1
The spark plug wires are routed in a tube or ducting. The spark plug leads can be replaced as a unit with the tubing or individually. Unplug the spark plug wires at the distributor cap for engines with a distributor or at the coil pack on the M42 engine. The M50 engine has no spark plug wires as the coils sit directly on top of the spark plugs. Mark the leads as each one is disconnected to correctly refit the wires. Original equipment wires and distributor caps are marked with the cylinder number, making the installation easy.
Unclip the spark plug wire duct or tube and remove the wire. Replace the wire in the same routing as the old wire. Be sure to match the wire number with the distributor cap number or coil pack number. Snap the ducting or tubing together.