My original speed sensor had the small circuit in the pig tail, but the new/used one I bought off Ebay PN 4011111 does not have it. I did check the voltage like you suggested and I never got a reading or surge in voltage. I'm thinking I bought a lemon from Ebay.
Lol....thought it said 05. Sorry.
Basically it is an AC wave generator. You should be able to put a meter set to ACV on the wires, Jack it up, and spin the tire. If it works. Then it will produce voltage. Is there a small circuit board in the pig tail?