Modernized Engine Wiring

Diodes--I see so you are using the forward drop in each direction to form a wiring shunt.

So far as wire ampacity, I resist the temptation to over-rate smaller wire. After all, wire (in cars) isn't all that long, and therefore is not all that expensive. Voltage drop figures in vehicle wiring should be held much tighter (percentage) than 120V/240V building wiring

Besides, after fighting for years with Mopar "small wire" in tail lights (adding a trailer!!) the bulkhead connector, and the "was always" too light headlight wiring, I'm more than willing to "not downsize" wire gauge.

A good example of this was my old 70RR, which had 4 tail/ turn lamps, and I did do some trailer towing. So you have 4 stock trail lamps, plus the clearance and trail lamps on the trailer --all run off the flimsy stock Mopar wiring.

Over the years, most of my old RR got re-wired with nothing smaller than no14. I had lots of it.