First the red wire/battery fuse should be 30A. Fix that. Make sure the battery is connected correctly, generally the white wire is the negative, the wire with a fuse/breaker is the +. Second, disconnect the battery and measure the voltage from the converter near the battery. Then measure the battery itself to make sure your meter is working then remeasure the converter leads. 12v is not enough and indicates an issue, you can measure the WFCO's output at the back of the WFCO itself (disconnect the red wire on the back of the WFCO, this is the 12v+ in/out from/to the battery, there will be a white 12v- wire there also).