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Mazda B2600i lights and voltage buildup on outside of wire between distributor and ignition coil

My 89 Mazda B2600i conked out on me suddenly about 10 days ago. My local mechanic replaced the distributor, cap, and rotor and the ignition coil and now it’s running again. But starting it up at the mechanic’s, I noticed a new faint sound like a clock ticking rapidly. From under the hood it sounds more like an exposed spark plug firing, but fainter. After driving around to make sure I wasn’t imagining it, I had the mechanic take a quick listen and look. He couldn’t say for sure what it was, but said it was probably nothing to worry about.
Taking a look under the hood at night, I saw lights running along the spark plug wires (continuous) and flashes of light where the spark plugs insert (frequent). If one terminal of a volt meter is placed on the outside of the wire running from the ignition coil to the distributor and the other held in the air, the voltage rapidly builds up to 4 volts (a few seconds) and then immediately drops back to zero. This happens in roughly the same time frame as the flashes of light where the spark plugs insert, but I can’t tell if it’s the exact same frequency.
Any idea what’s going on?

You seem to need new plug wires.

It’s exactly like an ecposed spark plug firing. Some of the spike from the coil is arcing to the head, which is an electrical ground. The pretty lights you saw were the arcs.

Change the plug wires and the engine will run better…and quieter.

I’m a bit taken aback that the mechanic didn;t know immediately what the problem was. This is about as basic as it gets.

I’m a bit taken aback that the mechanic didn;t know immediately what the problem was.

I knew a real good mechanic that would sometimes miss something like that. Turned out he had not hearing above 12khz. There would be no way he could hear that ticking sound.

You’ve discovered that darkness can be a great diagnostic tool. It’s a lot more comfortable than touching the plug wires with your hands. Any mechanic can assume that the plug wires aren’t a cause because the things are a lot better than they were years ago. That was when the problem was “always” the wires.