Originally Posted by dholaday
It's been said earlier in this thread but it's worth repeating: When choosing a wire gauge consider not just the amps a device will pull, but also the TOTAL length of the run - i.e., from battery to device to ground.
On a sidecar rig, that could be 15 feet or more.
Note also that the chart DRONE posted [and that was included in my link in first post] is for American Wire Gauge - AWG is a little more robust than automotive SAE gauge wire.
You might also choose to use marine wire - it comes in AWG and the strands are tinned to better resist corrosion; again, a little more robust than plain copper strands.
I'm considerably more conservative than DRONE when it comes to wiring - I'll move to one size larger [or maybe even 2 sizes] than recommended just for my peace of mind . The difference in cost is negligible.
Ask The Google for marine wire - there are LOTS of sources, including Amazon :-)
One of the things I still haven't figured out is what adding a bunch of additional stuff to the bikes OEM wiring does, if anything.
Regarding the AWG wire and SAE wire, AWG American Wire Gauge wire is specifically designed and made for Residential, Commercial and Industrial applications. SAE wire is for vehicles. Marine Grade will have other specifications added for further safety. AWG is much thicker strands made of different copper alloys than SAE. AWG has fewer and heavier gauge strands in a given wire gauge size than SAE does. Conversely the SAE has more strands of a lighter gauge in the same 'Gauge' rating.
The AWG wire is intended for the express purpose of being used in permanent, static non-moving applications, often run inside conduit and securely fixed to prevent any movement at all. The alloy in AWG is not designed to flex, is less malleable. When run in conduit the conduit is placed with whatever bends in it, then the wire is pushed or pulled through, making those turns and bends, one time. That's it for its lifetime, never intended to be moved [flexed] again.
AWG wire also has several classifications such as TW, THW, TWN, THWN, THHN etc. which are specifications for a particular purpose and use. This is worth investigating to know what type of wire you're actually dealing with. These can relate to the conductor's alloy and the plastic sheathing layers on outside plus temperature. The plastic sheathing coating on AWG wire isn't friendly to light or ozone and hardens much more quickly than SAE wire which remains far more flexible for a much longer time.
SAE wire with fine, thin strands is designed to be used in applications with movement, vibration and possibly temperature changes. The fine soft strands are more forgiving of flexing and the alloy is such to withstand flexing without work-hardening much moreso than the AWG stuff. Vehicle use also requires more hand manipulations of the SAE wire during initial installation and it's often moved and flexed several more times in its life in order to facilitate troubleshooting and repairs so it's simply made to be more flexible throughout its life.
Similar example is wire used in extension cords. Cut one open and you find super-fine strands, lots of them. That's because extension cords are specifically intended to flex around whatever and wherever without becoming work hardened.
Also regarding solder, note that there's all kinds of different alloys, some very hard, some very soft, some with specific properites for specialized applications including different fluxes in flux core. Some of these alloys may have a chemical reaction with disimilar metals and cause rapid corrosion and conductor failures.
Another note: Residential/Commerfcial/Industrial wire tools for AWG wire do NOT work on SAE wire because the extrenal size of a gauge is different. You end up with nicks and cuts in all the outside strands in a conductor if you use the wrong type of stripper.
The proper wire with the proper solder and flux, or else proper wire with proper connectors and assembly technique, using the right tools make all the difference in the world, especially at 10PM in the dark in the rain in the middle of nowhere.