It is the wire construction itself. The metal ends have, for all practical purposes, no resistance whatsoever.

If you want to test yours, remove the wire from the car, select the ohm range on your multimeter, calibrate if necessary, then one probe on one end of the wire, the other probe on the other end. Polarity is irrelevant. Then read the resistance. Compare your reading to a metal object (a key?) to see what virtually no resistance reads. All of your wires should read similar to each other, but note that longer wires will have more resistance.

It's hard to find non-resistor wires, but it's possible, and since it sounds like those were homemade, maybe so in your case. Another easy test is radio static, since that is a principle reason they use resistor wires in passenger cars.

Hope that helps.