If this is for a GRP car it is worth running a set of earth wires in the loom. One of the issues with kit cars using existing loom wiring was earthing. My solution was to run a flat heavy duty copper strap from for to aft and engine then bring things to it. It made fault solving and modification a lot simpler as there was always an earth nearby. That would now be expensive. It solved issues on my Mini Marcos and many later weird monstrosities with half or no chassis or aluminum bits which would corrode if linked to a circuit.
Cars without fuses, or adequate fuses. Certainly this was popular and ran on late in Britain. Another reason why German cars were better as the had more fused circuits and if the worst came to the worst you could iscolate the duff sub part of a circuit, wire the rest in somewhere else and get home in relative safety. With two or less fuses that starts getting impossible. Also the chances of fire are greater. I have had Isetta, Frogeyed Sprit and TR7 spontaneously combust from a loom fault on unfused or inadequately run wiring. The Heinkel was a failed Siba regulator, which should not even have been there - British quality again, and the Lloyd Bus, a blow back through the carb to a total loss.
So no fuses, do not run an earth wire in the loom as you are offering an overheated wire a short circuit once the insulations failed and then you cannot always turn it of. The same will happen if it finds a lighting wire or something but normally its not a direct short but through a lamp or something which limits damage a bit.
Have we all had a welded car which had a melted loom. Put the wipers on and the left indactor joined or some such. Yep, been there. Schmitts are good for that where the tube wire has been compromised.
