wiring a transformer

[thunderchicken]

I bought a 120 volt ac to 24 volt ac transformer from radio shack and the wiring is confusing the hell out of me. the 120 side is simple two wires but the 24 side has two yellow wires and one black. if i test yellow a to black i get 12v and if i test yellow b to black i get 12 and if i hook the the two yellows together it starts humming loudly and gets really hot really fast so i think its shorting. anyone know how to wire it to get 24v? thanks

[OLDHEAD]

I bought a 120 volt ac to 24 volt ac transformer from radio shack and the wiring is confusing the hell out of me. the 120 side is simple two wires but the 24 side has two yellow wires and one black. if i test yellow a to black i get 12v and if i test yellow b to black i get 12 and if i hook the the two yellows together it starts humming loudly and gets really hot really fast so i think its shorting. anyone know how to wire it to get 24v? thanks

Oldhead here.....24 volt should be between the 2 yellows.The black is a center tap on the 24 volt side(12 volt to either yellow) Hooking the yellows together is a dead short(Not a good thing to do),For more info. pm me .....OLDHEAD

[thunderchicken]

thats it thanks