Buying many spools of new wire would be very expensive. For my under-hood rewiring I used special 20 awg colored ribbon wire for everything in the bulkhead that now switches relays. That keeps the wires ordered. You can't get that, so might use common 28 awg "computer" ribbon cable (a bit wimpy). For other wires (turn signals, ...), I used trailer wire and pulled from my "scrap wire box" and the partial harness I pulled with the relay box, plus a 74 Dart engine harness I had. Whenever I discard an appliance, I try to save all wires and connectors.