We use solid core wire on sets that have resistor connectors.
Our Wire wound cable has 500 ohms of resistance and is used when the connectors have no resistance. (Jag, Volvo and MG)
Copper core wires have no resistance so the connectors do. (Mercedes and VW) Most European wires are copper core.
Most wires are special made so there may be some wait time before shipping. In most cases approx 7 working days. If they are in stock they will ship with the rest of your order.