Wiring is now a critcal part of a modern competition car, it is no longer the last thing that gets paid any attention.
Reliable wiring and connectors are now critical.
Motorsport has followed aerospace in wiring specifications and best practice, modifing the requirements in the last 20 years or so. So while there is plenty of "mil- spec " wire out there make sure you look out for :
Kiwi Connectors stocks Raychem type 44 and 55. Rated to -65 -150 degrees.
Prices vary between colours. White is always the cheapest option.