CR104B Vehicle Electrical And Mechanical Systems Practice Test

The key idea is that the fuse protects the circuit from overcurrent, so a motor that draws more current than the circuit is designed to handle will blow the fuse. If the new blower motor has lower winding resistance than the original, it pulls more current at the same supply voltage (Ohm’s law: current = voltage / resistance). That increased current can exceed the fuse’s rating and cause it to open. To check, compare the new motor’s winding resistance to the spec for the original motor; a significantly lower reading or a shorted winding confirms why the fuse trips. While a defective fuse, damaged wiring, or a stuck switch could cause problems, the most direct and common cause after replacing the motor is a lower resistance in the new motor leading to higher current draw and a blown fuse.