Originally all 5 wires there are 12 gauge, yellow for starter relay, brown ign 2, red 12 volts input, blue ign 1, black accesories. However I think the only wires really needing 12 gauge could be the red one and maybe black which runs to fuse box Acc buss bar
Yellow becomes on 16 on engine bay without any other splice around and is just a trigger signal for the relay. So I never understood why 12 there
Blue and brown becomes on 14 on engine bay, but blue sources some small load stuff around before the firewall, like idiot lights, brake light and in some models the VL on cluster for the gauges, some others are sourced from acc. On 71/74 B bodies, VL is sourced from Acc on Rallye clusters, while on standard clusters is sourced from Ign 1. Some other acc could be feeded from Ign 1 too like hideaways, powered trunk latch and stuff like that
Blue could be another one to keep it 12, specially using aftermarket ignition/fuel related devices.
More than the gauge wire on these, is better to take care of the best terminals/conectors, which on this plug could be the weakest point. 72roadrunnerGTX posted quite ago a great terminal/plug set up for these used on his car, which I had found it quite ago but didn't know they were stackable untill he shown his car setup, which make the assembly work and look like a stock setup and keeping the order there. If I found the pic &/or the terminals will post. Maybe he will read and post by himself before I post.
