You should be getting 12V at the puck. Double check your meter's ground connection. Test at another working light to verify.
Also, are you getting 12V at the "incoming" side of the switch (supply side) with switch in off position? If no, then problem is before the switch. If you are getting 12V to the switch and then when you turn it on and measure the output side of switch (load side), if that's where your reading 3V, then problem is on that side of the circuit.