... or a hard-starting scenario, bad starter or battery, or a malfunctioning regulator. Far better to have the capacity and not need it rather than the other way around.
Say you come out to a dead battery for whatever reason (left the lights on, etc). You get a jump start from a friendly stranger, or the AAA guy, what happens after they disconnect their cables after your engine starts? What does your alternator do? Steve is right, better to have the capacity and not need it, than the other way around.
Bones for you and Blues4u, I had a Old Air Products Hurricane installed. The 4 feed Vintage did not want to fit under my 56 very well. A 3 feed may have but the shop didn’t have one in stock. The guy doing the work suggested an OA. A good friend has one in his 56 Ford Courier which is a big empty box and never uses high so I said go ahead. The Hurricane works different by having the fan on the opposite side of the evaporator than the VA. Rather than blow thru the evap is sucks the inside air by the evap. It also fit. I have the electronic controller and split the air between the main vents and the 2 defroster vents. This is my first summer with it and so far so good. Idling in traffic with it on I can get to 205* which so far is not a problem but I did add a rad overflow and a13 psi cap where I had a 7.
Not much of what you listed applies to the main power feed wire. Since that wire is usually short, and rarely bundled with other wires, the derating, or loomed derating would rarely apply. And even with conduit, or other wire enclosures you don't derate until you've got a certain number of wires. I doubt you'd lose any current rating with the average 6'-10' main power wire, and very few places it would ever be bundled. All the wiring harness kits I've ever purchased never had more than a #10 main feed wire in them.
Which is why I'll never buy an aftermarket harness kit for anything other than a 'bare bones' car and is the reason some guys have to use relays when powering headlights. Vintage Air is also aware of this shortfall, that's why they recommend powering their systems through relays, not the fuse panel. Low voltage is hard on the electronics. In their defense, the OEMs that they mimic can be just as bad. A buddy has a mid-60s convertible with a power top, seat and windows along with AC and none of that is fed from the fuse panel except for the relay control power. The OEMs do this so they don't need multiple harnesses. Build a 'standard' harness then add 'sub harnesses' for each system. This works, but you now have relays and circuit breakers/fuses scattered around the car and multiple power wires connected to battery power. Very easy to fix on a custom harness, not so much with a 'one-size-fits-all' kit.
I like to get a tripple maxi fuse holder and put it close to the battery. Run 2 #10 wires fused at 30 amps. One goes to a 40amp relay the other is always hot. You can see the wires to the maxi fuse holder here. I sleeved the #4 red after this was taken Run those into the car under the dash. I get cheap 14 fuse holders (divided into 2 sets of 7) one set (7) is hot all the time, the other 7 are fed by the relay and hot when the key is on. I then use the ignition switch as just a pilot device to run the relay, and radio in ACC. Now you have a spare maxi fuse for the alternator, or a stereo, or that A/C evaporator. I use a small fuse/relay box under the hood for engine and lighting. I like to use XHHW wire for everything, as it takes heat very well. I keep all things separated and can run #14 wire for pretty much everything. This makes every old switch only have to carry the load of a relay coil or two. I fuse all old switches at 5amps. I've wired several cars this way. Basically the only unfused conductor is the short run to the maxi fuse holder. I hid it in the fender in my 59, so about a foot from the battery.
In the early 70s maybe late 60s GM started using #14 fusible link to 10ga wire. Fusible link is slow blow. To replace or add it you crimp it on with a but connector link to wire and then used self sealing heat shrink tubing to make it weather tight. All is available at your local NAPA dealer. That’s how we did it at Buick because Buick told us to do it that way.
The only relays I've ever used on my builds were for electric cooling fans, or electric fuel pumps. Never had any issues with my cars wiring systems.
Interesting...just about all production items that have electric parts in them, used crimp connections. I've never had trouble with crimped connections in cars, on stuff that I've done. I have had trouble with crimps that others have done. I guess there's a pretty big learning curve? Or maybe some folks think it's simple, and don't take the time to learn how to do it well? I don't know. If you can't make reliable crimps, but you can solder well, then soldering is the way to go. Just make sure you can solder properly...there are lots of way to go wrong with it, too.
I like to use 10 gauge or 8 for my main line. @squirrel is totally correct on his fusing recommendations, of course my brain is saying "why wouldn't he be" he is a damned good mechanic. I have a tendency to use a 30 amp slow burn fuse on my main line. Even if I am using 8 gauge. Unless I am mistaken GM used a 30 amp fusible link way back when. I also do not run all my constant hot though the ignition switch. I sometimes run lights that will burn the night at way over the speed limit. The ignition switch won't handle the stress or at least my feeble mind don't think it will.
Lol... I recently had to pull a buddies gas tank BACK OUT on an OT car for a bad crimp. When I gained access to the crimp, a slight tug pulled it apart. When I asked if he checked his crimps, he said " not like you do"... meaning he, like a lot of folks, gave them a gentle tug, fearing he could pull it apart. Bad logic folks. Yank it now before it gets buried. Better to KNOW that baby is tight.
Here you go.... Technical - Crimping Tutorial | The H.A.M.B. (jalopyjournal.com) Crimped or mechanical (screw) terminals have been the only legal (as per the NEC) method for field-terminating wire since the '50s if not earlier with a very few exceptions. Solder-only connections are only allowed on 'approved assemblies', i.e. factory built and UL approved. The problem with solder is it's melting point is between 360 and 450 degrees F, have a connection get exposed to overload or a loose connection and that amount of heat can be easily generated. The solder can 'move' before reaching that temp, causing the joint to fail quicker. The heat required for a good joint also makes the transition between the soldered wire and unsoldered part brittle, making it much more subject to vibration/flex failure. Very good strain relief at solder joints is critical. If you use shrink tube for strain relief, the tube thickness after shrinking should be equal to or more than the wire insulation thickness.
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