Plug Wire Rebuild

• $35 for 3m of lead wire ($3.55/ft).
• $13 for 8 feet of 1/2" shrink sleeve (I used 2 feet)
• Maybe a dollar or two worth of solder and butane

Total cost of materials actually used was about $35 (in 2025).

Disassembly

First we need to disassemble the wires. Everything is salvaged except the actual high tension wire itself.

Remove the brass plug clip that is threaded in on the plug end of the boot using your big flat blade screwdriver. It looks like a main jet from a carburetor. It will be springy as you twist the screwdriver because the only thing resisting the screwdriver is the plug wire in the boot. Resist the urge to clamp it in the vise, you will probably break the plastic holder the clip is screwed into. It isn't that tight, you'll get it. After it is threaded out you can grab it with needle nose plier and pull it out. There is spring attached to the end of it. Put the brass clip and the spring in a ziploc bag now before they grow legs.

Tap the ceramic resistor out that is right behind the spring. This little resistor is brittle and sits in a short length of rubber tube, don't dig at it too much. If it won't come out leave it, you can get it out later. I think three of my four came out easy. It is difficult to tap on a floppy silicone boot to get any impact to make it come out.

Now this is the "scary" part, getting the plastic holder out of the silicone rubber boot. This plastic holder is made of something that looks like Bakelite, maybe it is. I am amazed I didn't it on the first one when I didn't know what I was doing.

First off you need to take your 10mm x 1.25 bolt and file it flat on the end. Bolts usually have the first portion of the threads tapered. By filing the bolt flat you will ensure you get maximum thread engagement into the plastic holder. It only grips by maybe two threads and you don't want to rip a thread off. If you do you are hooped! If you do break it you could try getting one from a CBR600 boot, they my be identical but I do not know for sure. Just don't break it, simple.

Cut the plug wire off about 3/4" from the boot. This is done to avoid pulling the wire through with the shrink sleeve on it that won't really want to feed through the boot. Now take some 75% dish soap and 25% water solution and work it into the space between the plug wire and the boot AND in the plug end between the plastic holder and the boot.

Now thread your 10 x 1.25mm bolt in until it bottoms out. Don't crank it in, just thread in until it stops. Tightly clamp the head of the bolt into a vise. You are now ready to pull the guts out of the boot. I found it helped to put a tiny screwdriver in the plug end between the boot and plastic holder to help it get started. You could use a heat gun to heat the boot at this point and no harm in doing so. Try to more to push on the plug end of the boot and just a light pull at the big flanged part on the wire end of the boot (not on the wire, obviously). It makes more sense to push so the boot expands. Try to not put any side load on it or you could break the plastic holder. Also watch that any twisting you do does not unthread the bolt. If you have to twist it do it so it is tightening.

Now the plastic holder should be in your hand. Straighten out the stub of plug wire a bit and push it through the plastic holder. If you didn't get the resistor and it's rubber sleeve out earlier it will come out now. Push the resistor out of it's sleeve and dry them both and the plastic holder. Put them in the ziploc bag with their friends (the clip and spring). If you lose a resistor have a look at some of the NGK aftermarket plug boots that screw on to lead wires. I saw some disassembled on the web and they looked the same. The NGK resistors are also 5000 ohm, same as the RC30.

Do not throw the little stub of wire out just yet! 

The stub of original plug wire you pushed through the holder has a brass washer on it you need to salvage. It is difficult to tell what it is because it has a big blob of solder on the end. This solder holds the lead wire strands to the washer and provides a good contact for the resistor. Take note of how thick the solder is as a reference for later. This washer is just slightly larger than the 7mm wire and registers against a shoulder inside the plastic holder. Though it is quite easy to salvage I will nonetheless say how I did it.

I lightly clamped my butane pencil torch in the vice and set it with a good flame. Hold the lead wire in your hand and heat the solder to liquid then immediately tap it on the vise or something hard to remove the solder. Good idea to have safety glasses on doing this. Solder in the eye probably hurts. Do this a couple times until most of the solder is removed. You can now see the strands of the lead wire and how they are bent over through the washer. Take your side cutters and cut the lead wire strands off as tight as you can against the washer on the lead side. To get the little pieces of wire strands off the washer I held the washer with needle nose pliers, heated it again with my butane pencil torch and tapped it on the vise and the strands just fell out. You now have your salvaged washer, and as a bonus it is already pre-tinned.

There, you have disassembled it and hopefully all went well. You may be wondering what you got yourself into but fear not, it will come together. Below is the first one I took apart. You can see how I twisted the lead wire off (found out that doesn't work!) and I also pulled the strands through with the brass washer still attached (just because). I also had not yet filed the end of the bolt off as in the picture above. Do as I say, not as I do, would apply to this picture.

Preparing the Lead Wire for Assembly

Installing the New Lead Wire

Feed the pull wire (but not the lead wire just yet) through the boot. You must do this through the spark plug end. A slight kink at the tip of of the pull wire will help it feed through the boot. Before you pull any lead wire through the boot you must spray it with silicone spray immediately before pulling it through. The silicone spray dries quickly. Pull it through using the pull wire you soldered on so there is about 10" of lead remaining on the plug end. The silicone spray makes it slip through easily. I don't recommend using soapy water for this just because you don't want soap or moisture inside the boot. My Dad used to call silicone spray mouse killer because the can says "stops squeaks". The silicone spray also works as a cleaner for the boots, it took off most of the minor scum.

Cut the end with the zip tie off. Don't just cut the zip tie, cut about 1/4" of lead off also, the strands that were bent over need to be cut off so you start with new wire. Do not use the pull wire after cutting the zip tie off. The brass washer must be soldered on before the pull wire is used again.

PUT THE PLASTIC HOLDER ON THE NEW LEAD WIRE NOW ! Ask me how I learned this. The tapered end goes toward the boot. Don't push it into the boot just yet. It just needs to be on the lead.

Prepare your salvaged brass washer by sanding the tinned side until it is nice and shiny. Do not sand the solder off, just shine it up with some sandpaper. The old solder on there is a good thing.

Strip about 3/8" to 1/2" of the lead wire, leaving just the strands. If there are any glass fibers cut them off. Cut the insulation off perfectly square and DO NOT nick the strands, if you do nick them, cut that part off and try again. When doing this just pull the cut off insulation straight off, don't twist it or you'll have strands pointing everywhere. Place the lead wire in a vice so it the insulation is flush with the top of the vise, just the strands above the vise. Don't mash it, the vice needs to just hold it. Now slide the washer over the strands and let the washer butt up against the lead wire insulation (and the vice, as they should be flush). This can be a bit frustrating, reading glasses really helped. The tinned side of the washer faces up. Split the strands into two approximately equal groups and bend them back to lay against the washer just like the original was when you unsoldered it. Don't mess with them too much, you will just break them off or weaken them. Bend them over and stop.

You are now ready to solder the lead wire strands to the washer. If the strands stick past the washer that is fine, just leave them. The easiest way I found to solder this was to coat the washer tinned side and strands with a bit of flux and place a cut length of solder on top with a bit of flux on it. By using a cut length of solder you are guaranteed to have the correct amount to produce the convex profile. I used 0.115" diameter solder and found that 5mm to 6mm of cut length was perfect. Now just take the pencil torch and melt it on. The solder should naturally form the convex profile. You do want enough heat that some solder will make it's way through the washer hole to strengthen the strands at that point. Let the solder cool naturally. 

Now take side cutters and cut off any strands sticking out. A small file can now be used to fix the profile of the solder and take off any pointy strands. Where the resistor will contact the solder I suggest a slight flattening of the solder. Use some fine sandpaper to finish it up. The convex portion of the solder should be about the same thickness as the washer. Check the OD of the brass washer and get rid of any solder that may have made it's way there. Don't remove any material from the brass washer. The OD of the washer just fits inside the plastic holder so any excess solder here will mess up the fit. The washer should now be soldered on and tight up against the lead wire insulation.

Slide the plastic holder down the lead wire. You should be able to feel when the brass washer contacts the shoulder inside.

Take the resistor out and check the resistance with your multimeter. The resistance is nominally 5000 ohm.  reading between 4000 ohm and 6000 ohm is good. Write down the exact reading. You will use this to check your work later. Put the resistor in it's rubber sleeve, center it, and drop it into the plastic holder against your fancy soldering work. Take the brass clip and spring and thread them into the plastic holder. Snug it up using a 13mm wrench on the holder and your big flat blade screwdriver on the clip. Again, go easy here, it just needs to snug. Breaking the plastic holder would be bad.

Don't push the plastic into the plug boot yet. Take your multimeter set on ohms and check the resistance between the brass clip and the end of the lead wire where the pull wire is soldered on. You should get the exact same ohm reading as what the resistor reading was. If not, check to make sure everything is assembled correctly.

It is time to pull the plastic holder into the plug boot. This isn't too difficult but you want to make sure you don't twist the lead wire too much or yank on the pull wire too hard. Because the silicone spray evaporates quickly it needs to be done reasonably quickly. I coated the plastic boot with a very thin layer of silicone grease (left over from a brake job years ago). Don't use anything but silicone high temp grease. Now spray the lead and a bit inside the boot. A tug on the pull wire should get it moving and once the plastic holder hits the boot use a combination of pushing the plastic holder and a light pull on the pull wire. It should slide in fairly easily, popping into the molded area inside the boot. You can see on the outside of the boot if it isn't fully home.

Re-test the lead using your multimeter. If your soldering survived you should get the same resistance reading again.

At this point you need to cut the lead off. I recommend cutting them long, you can cut it off later to fit. I cut mine 38mm longer than Honda did until I test install them. See the table below for the length Honda used. I got the same measurements from my old wires as I did from the new set I had in stock. This is measured from the boot to the tip of the lead. If your lead wire has finer strands (like mine does) you should cut the lead at least 5mm longer. This will allow you to strip 5mm of lead wire and bend the strands over so the pin inside the coil does not just push the strands into the insulation resulting in poor contact between the pin and lead wire strands. The Honda lead wire has coarse strands (only seven of them) so they didn't have to be that concerned about it.

After checking the lengths and making yourself happy with them put a length of shrink sleeve over the lead and put the plastic nut, backing ferrule and rubber seal on the lead. Again, a bit of silicone spray will greatly ease getting the seal on. The first part of the seal should be 40mm from the end of the lead wire. double check that the seal has the tapered portion mating with the plastic backing ferrule. Push the lead into the coil and snug the nut to the coil. It's just plastic so go easy, it doesn't do much. You could glue the seal to your new lead but I didn't, seemed like overkill when I looked at how the seal mashed the old wires.

After installing the wires on the bike use a heat gun go at the shrink sleeve until it is bonded to the lead. You may want to just get it started and following any bends then remove it and finish the shrinking off the bike. It is much easier to shrink it on when you can get around the whole wire.

Before you forget... strip the remaining lead wire and install the zip tie over the strands for the next assembly.

Here is a picture of the rebuilt ones, they are still longer than standard (see table below) and need the shrink sleeve heated.

Reference Information