My rig had a similar problem, but it was the GFI in the engine bay that popped everytime I plugged in the block heater. Does your block heater plug in somewhere? Can you fnd it and trace the line? Year, make and model helps us to help you, along with engine type and size. You can always go to Autozone and get a magnetic oil pan heater and use that. I actually have both; bigger is always better.