blowing down converter fuses

[spoiler1041]

my 48v to 12v converter blows fuse instantly. OK, a short. Was looking for a way to test for the short so I know when its fixed. Thought was hook meter to positive going into converter (now shorted out) then other probe to + on battery, I assume there should be no reading normally + to + but a short would complete the circuit through the converter. I get a reading so short is confirmed but I get the full 52v not 12v. So is the converter actually broke or is 52v expected?