Engine block heater

The only "block heaters" I know of are AC current units plugging into a normal household style plug outlet. There will be no fuse in the pannel for this because the pannel is DC current. If I'm speaking your type of unit to check if it's working use a volt/ohm meter and do a continuity check across it. Put your leads on the two flat terminals. You should get a resistance reading. If you get an OL display you have an open in the circuit. Could be bad plug, broken wire, or bad element. Also check the ground terminal. Put one lead one at a time on the flat terminals and the other one leave on the ground. This should read open "OL". Now check the ground terminal against the block heater mount. Should read less than an ohm resistance. Hope this helps.