THE UNIT HAS POWER. Most MKIII ignition units will produce a spark on switching on and off; if this is so and sparks are produced on all cylinders then the ignition coils must be in good order. If one or more fail to spark, a coil could be faulty. On four cylinder machines try disconnecting one coil at a time, and switching on and off, checking for sparks. On other machines the coils are used singularly or connected in a chain in series. One coil failing can stop sparking but if it becomes short circuit to its case the coils after it in the chain will stop working. It is possible that a working coil is shorting to case, and stopping the other coils in the chain from working. This is very common when a Lucas coil is over tightened in the metal clamp, the case becomes crushed and touches the windings inside. This can occur when the coil warms up. The Micro-MKIII, Micro-Digital and Micro-Power units all turn off when not being triggered, therefore it is best to carry out the next test as you may not always have a spark on turning on and off.