I've seen this before. One fuse on the positive lead for the pigtail wires to the DC power connector. Then there are 2 fuses at the vehicle battery end of the 16ft power cable. The best place to connect power to the radio is directly off the battery. The fuse on the negative side is to protect the radio and the car in case the main ground cable from the vehicle to the battery negative terminal were to become disconnected and someone tries to start the car through the radio's ground path. This is to handle cases of consumer stupidity and things that can go wrong.Why do they have 3 15 amp fuses????
One on the positive lead should be sufficient. Sometimes manufacturers will put on on the negative lead to make up for consumer stupidity. Trying to figure out what the 3rd 15 amp fuse is for?
In a couple of Volkswagen TDI (diesel) cars I owned years ago, this wasn't an issue because I used the 12V accessory outlet in the trunk area of the car. VW very thoughtfully wired the accessory outlet on its own dedicated 30A circuit with 10 gauge wire. It was just about as good connecting the radio directly to the battery. In this case only the single fuse on the positive lead on the radio's power wires was needed. No need to fuse the negative wire. There was no issue with alternator whine or other noise. There was zero ignition noise to worry about given that the car was diesel powered (TDI) which also made the car radio great for AM broadcast band DX too.