This wheel appears to be for a Maserati or Fiat (different spline count than a Mustang) with the horn button as a 12v switched single circuit to sound the horn, like an early '65 Mustang with relay. I believe these wheels had problems with catching fire due to the internals grounding and shorting. The little rubber washers on the contact ring deteriorate and you get a short. I have converted a quite a few of these for friends '65-'67's. You will need the GT350 center cap, a Mustang Grant adapter kit and the horn switch assembly which you can find from Fiat aftermarket suppliers. The only hard part to obtain is the steel outer horn cover where the button assembly mounts. These come up on EBAY every so often under Fiat horn covers. They make a nice wheel at a bargain price with a little work and when done look like the real aftermarket Shelby piece.