Spark Plug Wire Longetivy

Hello All, I hope this finds everyone well!

Back is 2016 I was getting Pole Cat ready for the Dearborn show and installed a set of Marti Works correct plug wires. By the summer of 2018 I had to replace the wires again due to arching. This time I tried the NAPA Beldon pro set or whatever they are called. The best they offer.

I have been insulating my pole barn this fall and winter so I never put the cat away so I could move it around in there. Finally finished, and last night I fired her up to put her to bed for a couple of months. I discovered a miss. I had been cleaning and such in the engine bay so I popped the hood looked around and decided to push on the plug wires at the dist cap. Yes, I got zapped. So I went and shut off the lights only to discover a light show going on under the hood.

I am wary of abrasion and chaffing, as well as, wires not touching each other, etc. In both cases, maybe 3000 miles clocked between the new wire sets. I don’t recall the plug wires being that much of an issue with these cars. Two sets in two years and maybe 6000 miles at the most.

Opinions please. Is there anything as an underlining problem that could cause this?

Thanks in advance, stay safe!

Edit: Pertronix ignition, BTW

Is the light show just around the dist , or through out the wires.

Hi Gary, I was having that trouble with the Marti wires on my Boss 302 Mustang. Installed the Pertronix wire set and cap seamed to solve it. Ran good all summer will see if that continues.

The light show was through out the wires. A little more on the drivers side.


There can be a glow around high voltage wires called corona, and it produces ozone which eventually breaks down the wire insulation over time. It is not ideal, but in a dark garage, I have seen it under some conditions even with brand new wires. What you should not see in the dark is sparks jumping to ground. This means the coil’s output energy is leaking to ground before it gets to the spark plug. Probably need new spark plug wires if this is occurring.

I’m interested in following this. Can’t shed any additional “light” on the problem but as a data point, I’ve been using Marti’s wires with the full pertronix setup including their coil on my 351C for several years without issue.

I worked on a car that was doing this (sparks coming off the wires) and found that they had increased the spark plug gap in the mistaken notion that it was a boost to performance. Regapping the plugs completely solved the problem. However, I have also found the boots on Marti wire sets seem to be very fragile. I have had them split and then cause issues.

That makes sense because the coil produces a higher voltage to jump the larger spark plug gap. But that higher voltage is able to jump other weak links too. Same experience as Bill on the Marti plug wires. Installed a brand new set of them in 2013, but the boots just fell apart last year when I changed plugs. The car was barely driven at all in those years. If boots or wire insulation are cracked, the spark can jump right out.

Yep, I found split boots on my Boss Mustang. I like the Pertronix wires better and they look somewhat correct. I’m going to stick with them unless it’s a correct car restoration.

Thanks for the discussion. My guess at this point is that I will change the wires regardless. I’m at least convinced that the zap I got is from a crack in the insulation. The corona intrigues my engineering mind and I will look deeper into that. Meanwhile, I plan on duplicating what I did last night and look harder at the sparks jumping and or glow around the wires.

Brian, the Pertronix components look to be a good quality and I will probably try them next.


In many instances “corona” is mistaken as spark plug flashover, however, corona is the glowing that appears above the plug “shell” around the base of the spark plug insulator. This condition ( more readily seen in the dark ) is caused by the electrical stress in the air adjacent to the insulator-corona is in no way detrimental to spark plug operation, and will cause a brown or grey deposit on the insulator top just above the shell. This is from a March 67 shop tips.

Sort of off topic. My dad was a Mercury Technician in 1939 and worked in a Ford dealership to pay for school until WWII intervened. So you could say he was old school and then some. He taught me a lot.

One thing he showed my brother and I was how you could use a long screw driver as a “stethoscope” to listen to where mechanical noises were coming from. You put the end of the handle to your ear and touched the tip to what ever you wanted to listen to. Works great to find a ticking lifter and so on.

So one day while trying to find a miss I get out this very long imitation Snap On screw driver that I used for this purpose. I had an idea which cylinder was missing so I thought “gee, the cylinder that is missing should sound different if I listen at the exhaust manifold”. Crazy enough that it just might work.

Now this particular screwdriver was the type that had what was basically a half inch nut on the top of the handle that you could put a wrench on if you needed more torque. Pretty handy.

The only draw back to my dad’s technique is that you have to turn your head away from what you want to listen to. So I poked the screw drive down to the exhaust manifold and started listening. Easy enough. Until I got to about the third cylinder back. The heater hose was kind of in the way and I couldn’t see clearly. Got the tip down on the manifold, turned my head and stuck that steel nut in my ear. I saw the flash as it turned my ear into a spark plug. Uncontrollably flinching from the shock, I turned my head to see what bit me, and jammed the screw driver into my forehead.

After bandages were applied. I recalled another old school technique. Look under the hood after dark for sparks, and never be the best ground.

Now there is a lesson that will never be forgotten! Funny story, although it probably wasn’t at the time. I worked on high voltage power supplies for aviation, and as tough as it to contain high voltage in our cats, taking it up to 40k ft altitude without corona is nearly impossible. Great discussion and I will look into Pertronix wires.

Al righty then, I’ll add some humor.

I have a wife who gets it and grew up in Detroit with cars and me. So when I told her what was going on she at least showed interest. After dinner I said I was going out to the barn to look at the car based on what we talked about here on this thread.

“What would that be” she asked. I said “I want to see if the plug wires are arching or if there is something called corona causing a glow”. “Would that be the coronavirus” she asked. She wished Pole Cat well.

Out to the pole barn I went and started her up. I thought, geeze (actually it was wtf) this is really rough. Shut off the lights and sure as sh$&, I see that it is arching. The worst offender was the coil wire shooting an arc about 1/2" to one of the intake runners. About once per second or two. I shut her down and went inside to refresh my vodka and water.

Marie asked how it went and I had to report that Pole Cat tested negative for corona!

I guess come spring I will be trying the Pertronix wires and cap. Still seems unusual to be going through wires like this.

Be safe!

Bill, your storys never seem off topic and are always a good read.

Another great story - enjoying the laughs. Pole cat looks like a really nice Cougar - glad it doesn’t have corona!

Here’s my favorite high voltage story - back when I was working on an aviation high voltage supply, my technician got zapped from 15000 volts DC. I heard a loud snap and came out to see if he was ok. He sat there with his eyes open, but had a completely blank expression and was speechless for a good 15 seconds. Slowly, his expression started coming back, and he jumped up throwing everything to the floor and screamed SON OF A B%#&!!! It was like his brain had undergone a complete reset, and powered back up mad.

So you don’t see the wires driving down the road! LOL. Why not use a QUALITY wire like MSD or this Motorcraft that looks close to original… color wise.

LOL, that could be the next thing, light up the wheel well with the plug wires.

That’s just it, I thought I was buying quality wires. The first set was like oh well. But I did a little research before buying the NAPA wires. A vendor/friend who races a 1/4 mile at a time recommended the NAPA as good street use. And Belden (as in NAPA/Belden) is one of the most respected cable building companies. We use many Belden products in every Spline roller that goes out the shop door.

The Motorcraft look like another good option. Thanks for the link.
Thank you for the kind words Calicat.

What kind of a spline roller uses wires? Just curious…

Not the spline rollers for screens. My company builds the machines that roll the splines on parts like your axle shafts. The common 28 and 31 Spline axles in our cars would have gone through one of our type of machine. From 2005, I think it was, and until they got the independent rear suspension, all Mustang flanged axles were splined on our machines. Robot tended cell with two of our machines. One running the 28 and one running the 31 Spline.

West Michigan is our website if you’re interested. Search West Michigan Spline on you tube and you can see the half shaft of a Caterpillar front end loader being rolled. I’m the old guy in the back ground swinging his arms like he is bored or something.

Got to got get the white stuff off of the driveway.