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How to make spark plug wires

Making your own spark plug wires is very simple.

It is also, however,
A fairly specific job relegated at this point mostly to antique motorcycles and Harley Davidson. But let’s be realistic.
There’s a hell of a lot of Harley and old machinery still running around,
So this is still a pretty relevant topic for many riders.

make spark plug wires


Here’s a few scenarios that are not exactly uncommon,
That would leave a rider high and dry for a store-bought solution:
  • You moved ignition component (Did you relocate the coil and now need longer wires?)
  • Mated items that never came together from a factory ( Do you have a different-from-stock ignition setup, Like maybe a magneto replacing a set of points? )
  • Desire a change in wire color, diameter, or material (Are red-and-blue wires not available for your red-and-blue machine?)

Step 1: Assess what you have and what you need

Like many things in life, foresight beats hindsight here. There are some things you may want to consider. I’m gonna list off a few important questions you’ll likely ask,
But it’s not exhaustive.

Wire – This seems obvious, but you have a few choices here. In the center of the wire is the core. Older motorcycles usually used copper-core wire,
Which offers little resistance, and you may see carbon-core wires, as well.

However, these wires can generate all sorts of electrical noise,
So suppression core wires were developed. You may see other materials used, too, like nylon or stainless steel. Different ignitions require different wire with,
Different resistance values and different insulating abilities. These can be manipulated in the spark plug,
The wire, the coil, and the plug boot, both intentionally and unintentionally.

The best way to make sure everything jives is to use what’s recommended what’s component supplier, be they OEM, aftermarket, or a mishmash, and understand that conflicts may arise.

The next item to consider is wire diameter. Usually this isn’t specified,
But larger wires generally offer less resistance and,
Thus better transmission of electricity to the sparking plug. Early spark plug wires are usually seven mm or so,
And later ones are often eight mm. Wires marketed for the hi-po look are often even larger yet, with 8.8 mm being a pretty common size. Harley-Davidson will even sell you a 10 mm spark plug wire,
And I’ve seen 12 mm wires available.

You should be aware that spark plug wires can help your engine,
Get all the spark the coil can throw at it,
But they won’t increase anything — at best, all wires can do is reduce losses. Moving outward, think about your jacket,

The visible sheathing that protects the wire. Most modern motorcycles utilize silicone jackets for this purpose. Earlier motorcycles used cloth-covered wire. And, of course, there are all manners of colors available.

Length is important, as well. Match what you have on the bike if appropriate, or run a string in the routing you want, remove from motorcycle, and measure. Remember that wire can come in sets. Also remember that if buying wires of a uniform length that you can trim down, but not add on.

Terminals – These are the fiddly bits at the ends of the wires — you know, where the wire terminates? The type of terminal is important. Some motorcycles, like 1970s Japanese bikes,
make use of integrated terminals and boots that also incorporate a resistor,
And at the coil end, they are merely jammed into the coil, where the core contacts a small spike. Some terminals are made to snap down over a spark plug. Other terminals plug into something, like a magneto cap. The “angle of attack” matters, too. Commonly, you’ll see 90-degree, straight (sometimes called 180-degree) and 135-degree terminals.

Boots – Boots protect your terminals from dirt and the elements,
And they also protect you from getting a snappy buzz should you come into contact with a terminal.
Most riders will want modern silicone or plastic boots,
Unless you’re striving for an antique look. These need to match your wire diameter and terminal angle. They also come in different colors and styles.

make spark plug wires

Tools – One difference between a pro job and a hack job are,
Quality tools and the knowledge to use them correctly. When it comes to making wires, almost without fail,
I have found tool performance is directly correlated to price. Remember, better tools will likely last you your whole motorcycle career. Amortize appropriately. There are fairly inexpensive plastic tools that work in a vise that Is serviceable (sorta). There are cheap-o “just get by” tools you can scrounge up, like electrical crimpers and strippers. And then there are the big-buck, “do-it-right” tools that cost a lot because they’re worth it.

Step 2: Cut your wires to length

Cut to fit. Run a little long if you have the spike-and-thread arrangement found on
Japanese bikes or a fold-back style; this will be most motorcycles.

make spark plug wires

Step 3: Prep the wires

You can use a small jig that allows you to cut through jacket and insulation without damaging the core, or you can use a good set of strippers to do the same thing. You may be able to carefully perform this task with a razor and some patience. Different wire styles will dictate how long to leave your stripped areas; double-crimped wires need far less exposed core than a fold-back style.

make spark plug wires

Install your terminal end at this time.You’ll want to put it in place and possibly even pre-crimp it, so the dies in your crimper can do the best job they’re capable of. If you’re using a spike-style terminal, you’d install the female threaded sleeve on the wire at this time.

make spark plug wires

Step 4: Fasten the terminal

Here’s the moment of truth. After you’ve got your wire terminal in place, you need to crimp. This provides a good mechanical and electrical connection. If there’s one time when the right tools matter during this job, this is it. An improperly crimped wire can cause intermittent ignition problems,
That will have you pulling your hair out.

make spark plug wires

Note different terminals will have different attachment styles. If you’ve got an older metric machine utilizing resistor caps and spike-style coils I mentioned earlier,
This may be the time where you screw down the spiked point into the female receptacle. In any event,
Your terminals should be fastened to the wires in such a manner,
That they are solidly affixed.

Step 5: Fine-tune

Make sure the terminal ends fit where they are supposed to. You’re looking for the sweet spot between “Man, that doesn’t even fit!” and “Ack, it fell off!” You can adjust the tension of the terminal a bit (carefully!) with needle-nose pliers.

make spark plug wires
make spark plug wires

Step 6: Install your boots

Put boots on the terminals. Some soapy water can make this part a bit easier. The boots serve to seal out moisture and dirt. They also prevent you from getting a zap should you come into contact with a wire or boot.

make spark plug wires
make spark plug wires

Note that sometimes this is easier before the terminals are installed,
And sometimes easier after. On my straight-style connectors,
It kind of didn’t matter, so I installed them before I crimped.
If, however, you were installing a 90 degree boot,
Those are definitely easier done after the fact.

make spark plug wires

Step 7: Spark ‘em up

Ground your plugs and check for spark or better yet,
Fire up your bike and go for a ride.

How to make spark plug wires
Ekster EU


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