30 Amp Automotive Fuse Circuit Tester - harborfreight This handy automotive fuse circuit tester has specially designed test leads that plug directly into your fuse box to quickly diagnose electrical problems. The tester can be used on all circuits up to 30 amps. Test leads plug directly into ATC blade-style fuse slots; Simplify electrical diagnosis; Protects automotive circuits during use4.2/5(34)Price: $14Brand: Cen-Tech® How to Test a Car Fuse Box for a Current | It Still Runs How to Test a Car Fuse Box for a Current by Bob White . An automobile typically has two fuse boxes. One, located in the engine compartment, is for the motor's electrical needs, and one in the cab of the vehicle is for accessories and lights. The fuses protect each circuit from excessive amps, which may damage the components.