No spark (well, one spark and then none)

[Richard Sargent]

I have a 1986 5000S which has developed an intermittent starting problem. It will crank merrily, but will not fire. Upon inspection, the grounded coil wire will spark once or twice, and then no more. I test-wired the coil's positive terminal to the jumper post, and was able to easily and consistently start the engine. It appears that the coil is not getting power. I replaced the ignition amplifier with another, and the car would still not start unless the coil was powered from the jumper post. Where does the coil get 12V from?

Does the Hall sensor play a role in supplying voltage to the coil?

Could a flaky ignition switch supply power to the starter, but not to the coil?

Could this be a poor ground for the ECU?

Could the ECU be toast?

I've seen similar symptoms in the archives, but no description of the cure.

I'm hoping one of you knows exactly how to remedy this situation. I'm presently tempted to install a new 12V supply to the coil, switched so I can control when the car starts. I'm thinking it might make an excellent theft prevention device.

Richard