The first thing I would do is a visual inspection of the electrical connectors under the dash, especially the one at the base of the steering column and for the ignition switch. Look for a blackened or melted spot on the connector bodies. It was pretty common back then to run into overheated terminals. High current causes heat when it passes through a little resistance between mating terminals. That heat causes more resistance which causes more heat until the plastic melts. When it is bad enough, arcing can occur between those terminals. The best repair for that is to cut the wire off each side of the plug, solder them together, and seal the joint in heat-shrink tubing. Never use electrical tape on a car because it will unravel into a gooey mess on a hot day.
If you do not find a connector that needs to be repaired, you'll have to watch where the arcing is coming from so we can figure out how to solve it. Look at which component it is connected to, and the color of the wire. It might take some time, but I should be able to find a wiring diagram if necessary.
If the arcing stops while the ignition switch is in the 'run" position, measure the voltage on the positive terminal on the ignition coil. Tell me what you find there. If you find zero volts or very low voltage, disconnect the positive wire, then measure the voltage on that wire. Here is how to get a huge clue that I can explain later. Measure that voltage with an inexpensive digital voltmeter and remember it. Keep the voltmeter connected, but also use a test light at the same point. With the test light added, the voltage will stay the same, go somewhat lower, or go to zero volts. Those voltages will provide a pile of useful information.
Also look for multiple wires melted together. Sometimes one gets hot and the insulation melts through where it's touching an adjacent wire. While much less common, it is also possible for a splice to be corroded. Those are usually buried inside the harness which is covered in a plastic wrap that looks like electrical tape. The arcing can melt that wrap and make it visible.
Sunday, July 24th, 2016 AT 4:56 PM