Wiring identification preference?

The neatest labels will be the ones Dana posted.
IMO they will not last that long. But just the process of labelling may help you remember how its hooked up. When you label, spend some time with the wiring diagram. That way you'll really learn how the circuits are connected up. The system is pretty simple once you get to know it. In fact that way you can use the wire codes rather than write out a description. R6 is alteRnator output, H1 is Horn power, etc

Señor Ding Dong said

View attachment 1716247507Well, this is what I’m trying to clean up. A lot of sketchy splices and fires waiting to happen. And this engine is likely temporary, I’m planning on a mild build 360 in the future, so having everything labeled and safe for the next time I engine swap is kind of why I’m even thinking about this.

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We've seen worse, but yes fix it up. I don't think white is factory. Starter solenoid feed should be brown and shouldn't need the addition connector, etc.
I don't see the fusible link. You can buy that.

DMT has new foam seals for the bulkhead connectors if '66 is the same as '68+
There's been some threads on making good splices as well as selecting and crimping terminals.