On most 12v fuses, the two main metal pieces have a small opening in the plastic over that you can insert the prongs of a multimeter. $3 or free harbor freight multimeter on the ohms or volts setting is fastest way to check fuses. On ohms, just make sure the main dc breaker is off or battery disconnected. With the meter on volts and main dc breaker on/batt hooked up, you just hold one side on ground that all the black wires are connected to, on the red just probe the fuses on each side of the fuse. Test lights makes this extremely fast. On ohms setting a prong is held on each side of the fuse. You are measuring resistance(impedance) 1 indicates blown fuse and 0 indicated good. On vols setting you want 12v+ on the meter or a beep from test light on both holes in fuse.
Correction: Your meter may vary. You may need to remove yhe fuse for testing on ohms. I am not an expert.

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