If its intermittent and the rev counter has never worked i would be looking at the green wire as mentioned above.

If you connect a testlight to the battery positive and then remove the green trigger (-) wire from the coil and put the other eng of the testlight in this. When you crank the car over the testlight should flash. If not then you know the wire (or ecu) is at fault. You could pull the rubber boot back on the ecu connectr and test the wire there, if its ok then there is a break somewhere in between.

This happned to a mates erst, rarther than pulling the loom apart all i did was cut the green wire at either end (ecu & coil) and run a shorter wire between the two around the back of the battery just to get it going again.