Did you replace the block heater yourself ?
The heater is located below the turbocharger and you should have no problem tracing it's power cord back to the outlet. Some coach manufacturers have the outlet in the engine bay by the radiator on rear rad RVs others , have the outlet in the power cord bay.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.