Gauge is "everything"....
Here's another thing that many people do NOT do when choosing wire size -- the "length of the run" is actually supposed to be measured as a ROUND TRIP... So if the physical distance is 5' -- The gauge really should be chosen based on the wire gauge chart as 10'. Most people don't know this little known factoid. I discovered it when choosing some wiring in my boat.
I think we get away with this in the car hobby/world - because typically you're grounding near the 'load'... so aren't really running a separate ground as you would have to do in a boat. But after learning this - I always "err" on a gauge up rather than the "minimum".
A quick calculation of wiring to show VOLTAGE DROP -- using 16 gauge wire - running 5' physical feet (for calculation purposes this will be DOUBLED) - a 12vdc load - 25 amp max - the VOLTAGE AT THE END OF THE CIRCUIT will be less than 11V when loaded.
Simply using 12 gauge instead - will net you 11.59 (11.6)V
This doesn't seem like a big deal -- until you actually use the load - and see the effect.
Of course that voltage will / should increase well over 12V while the alternator is humming along... but then again...
We're running ever increasing loads (almost constant loads) in our cars these days. EFI - Dual Electric fans - A/C - Stereos w/amps - electric fuel pumps and on and on... and I've seen alternator "charge" wires that are only 10 ga... and they're running a 120 amp alternator...
