I then set out to check my notes. Given that it was a fairly hectic and somewhat emotionally taxing point in time for me when they were written, I wasn't at all surprised when I discovered that they took off for parts unknown. "No big deal," I said to myself. "I wired it up before, and I'll do it again."
I found that the quality of work I did when wiring the ignition circuits was a direct reflection of my state of mind. That is to say, after I finished peeling away the multi-layer insulation armor I had made with silicon tape wrap, heat shrink, and asphalt sleeve, I was greeted by wiring that looked like pure, unmitigated crap. From excessive heat shrink covering inexplicable butt-joints, to using marine wire not suitable for the conditions I intend to protect against, I was left dumbfounded, embarrassed, and finally relieved. Relieved that no one else would see what kind of half-assed work I was apparently capable of.
Situations like this are good opportunities to learn, though. When cutting out the diode that I decided should be in (instead of putting connectors on each end and securing it in a place where it could be serviced without hacking into the harness), I discovered what my lesson would be.
The improvised "butt-connector" was used to join the diode lead to the wire shown in the picture. Despite my propensity for doing stupid things, I'm certain that the wire didn't look like a urinal penny when I smashed that joint together. I'll skip over the details of my investigation into the cause -- which are too boring for even me to cover -- and let you know what the cause was: solder. Specifically, the flux in the solder.
See, I prefer to double up on my wiring termination by crimping, then soldering my joints. The reason for this is mainly to serve in preventing corrosion. The crimp provides the mechanical joint (reminder: except for when it is, solder isn't a mechanical component!), while the solder ensures that the components in the joint maintain continuity and are sealed against moisture ingress to the stranded wire core.
When soldering these joints, you always use electrical solder. Not acid-core plumbing solder, or whatever the hell else. Trial and error led me to discover that the best solder to use for my wiring is actually low-temp soldering paste used to solder SMD components to circuit boards. It comes in a syringe, you can squeeze out just as much as you need, where you need it, and you don't have to spend a hand on holding solder wire. You can also get it to flow easily with a pocket torch, which makes it great for field repairs. All in all, it's fantastic -- so long as you use it right.
Electrical solder uses rosin flux to strip away metal oxide layers, wet the components, and allow the fluid metal to flow. While rosin isn't an acid flux in the way the term is used to describe flux, it is still acidic. Because of this, best practice when building soldered circuits is to wash the board or whatever with a cleaner (alcohol or some mild solvent) to remove residual flux. Even though I had cleaned this joint after soldering, this still happened. What gives?!?
Well, it's pretty simple: this was a result of what was basically a cold joint, meaning I didn't cook it long enough. The flux used in SMD paste is actually designed to neutralize once it has come up to soldering temp and stays there for a duration roughly equal to what it should take for you to do a properly-flowed solder joint. Since I didn't let it cook long enough, the remaining flux wicked into the wire core (probably even aided by the solvent wash I gave the joint after the fact), made itself at home, and proceeded to eat everything in reach.
At this point, you may be thinking that it'll be a huge pain to fix any other joints like this, but that's not actually the case. Like I had mentioned, the flux is supposed to strip corrosion away from the base metal when it's heated. If you re-heat it and reflow your joint, not only does the flux remove the corrosion, but everything should be neutralized after the joint is properly done, meaning the fix is as simple as hitting it with a torch for a moment.
It's pretty refreshing to find a screw up that is actually simple to fix, for a change. I'm going to get back to work so I can make others that are closer to my comfort zone.
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