Wire Splices

Jim Van

Jim Van

Joined
Sep 10, 2011
Messages
2,199
Location
West Michigan
Bike
'98 ST1100
Just thought I'd pass on an experience I have had with splicing wires.

About 8 years ago I made a set of 4 inch handlebar risers. I then needed to lengthen the wires going to both handlebar switches. I used a standard soldered butt splice, like the right splice shown below. Everything was fine until about 2 years ago. I had a problem with the starter turning over, but no spark. It turned out the one splice for the run / stop switch was broken where the end of the solder met the unsoldered wire strands. I made a repair and everything was fine until a few weeks ago. I went out to start the bike, but the starter wasn't being energized because of another broken splice for one of the wires going to the starter switch. I repaired that break but then the headlights weren't working. Yup, another broken splice for the wire going to the N/C contacts in the start switch. Apparently while repairing the splice to the start switch, I stressed the splice for the headlights and caused it to break.

So all the splices were failing where the solder stopped at an end of the splice. Apparently, this is a stress point and will fracture eventually over time. Unwrapping the electrical tape from the bundle, and moving the wires around while repairing the broken splice caused the other splice to fail.

So I re-did all the splices, but used the left splice shown below. I think this technique will be more reliable for a longer period of time. the splices were covered with two layer of heat shrink tubing. I'll report back in 10 years with an update ( if I'm still respirating at that time ).


Splices.jpg​
 
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I did that when I added high-rise bars to my first two bikes ('72 CL450, '73 CB750), both of which had the wires inside the bars, so the splices had to be thin. I cut wires around 10" long, and cut each bike wire staggered by an inch or so to make sure the bundle would be smooth.

I used heat-shrink tube to insulate each splice, then carefully tape-wrapped each bundle, making sure the wires remained parallel, again to keep the bundles smooth and thin. They went back into the handlebars easily, with the end temporarily taped in a taper to a pull-string.

l also butt-soldered each splice as you did, but having been into electronics since I was a kid, was in the habit of making sure solder flowed into the insulation a bit. Also, being inside the bars, my work didn't have to deal with constantly being flexed like external wiring would.

To respond directly, it is a known occurrence for flexed wiring to break where the solder ends and concentrates bending stress. That's one reason you often see terminals with heat-shrink tubing extending over the wire where it leaves the terminal.
 
For best reliability - do not solder. It makes the wire and the splice brittle, which is exactly NOT what you want on a part of a harness that flexes. It wicks up the wires and reduces the flexibility and strain tolerance of the wire. Use a good UNINSULATED compression splice, properly crimped with the correct crimping tool, and finish with a length of adhesive shrink tubing over it. An uninsulated connector is preferred because it crimps better. You can't correctly crimp an insulated connector. Yes, you can mash it, but you do not get correct and uniform compression. Adhesive shrink tubing is used to create a gas seal and prevent future oxidation.
 
Use solder sleeves, they have been discussed here several times. If installed properly, the splice will last the lifetime of the harness. They have been used in the manufacture of aircraft harnesses for decades.
Problem with either method is the excess twisting I see of the bare copper conductor. Copper work hardens and tight twisting prior to soldering will eventually crack adjacent to the solder flow if it can flex.
 
I've long stopped soldering wires on my bike if there is any chance there will be flexing at or near the soldered joint. If the soldered joint is going to be subject to flexing or strong vibration there's an increased chance of failure over a crimp.

That said I just checked out solder sleeves:


They could be very useful anywhere you can use a heat gun or meth user approved butane lighter without melting anything else. As long as the vibration at the bare wire/soldered wire point is stable you're golden. These seem pretty slick.
 
I prefer the dimple type crimp tool - Thomas and Betts, Ideal, Klein all make these crimpers. I've seen too many of the smooth squashed crimp sleeves that were loose to trust them. These were always on solid wire, done by unknown tradesmen, but all poorly done. I've never seen the dimple type that was anything but tight and secure. The dimple crimper can be used on insulated splices, but pressing that little 'finger' into the butt splice damages the insulation and you will be back to heat shrink tubing over the splice.

Soldering is the splicing method of choice - but only if there is no movement of the wires. Otherwise it is just about guaranteed to break as noted in the OP's post. @Jim Van's second splice should last a long time.
 
The interesting thing is the handlebar switch wires receive very little stress or movement where the splices were located. That's why I think just twisting the wires together and not using a crimp connector will be reliable. And I had the wire bundle wrapped tightly with electrical tape and tie-wrapped to the handle bars to secure the bundle. But over time, where the solder ended, fractures developed. The little I moved the bundle when repairing the last break was enough to cause another old splice to fail.
 
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