Very simple. Never connect Negative directly to battery and never fuse the Negative as doing so is extremely dangerous. Doing so puts your radio in Parallel with the Battery Bonding Strap to the chassis. That means a portion of all the automobile electronics systems current is flowing through your radio including the Starter. Secondly will bypass the vehicle HFE current sensor in the vehicle battery bonding jumper.
If anything were to happen to the vehicle bonding jumper, means your radio is now the bonding jumper. Put your key in the ignition, all the lights, bells, and whistles come as normal. Turn the key to crank your engine, and your car fills with smoke and fire. All that starter current flowed right down the Radio Negative Battery lead, through radio chassis and circuitry, and out the coax shield completing the circuit burning it all up along the way.
Not only is it dangerous, with a portion of all vehicle current flowing through you radio is called Common Mode Noise, Can be bad enough to render your radio useless.
The proper termination points for Positive and Ground. For Positive directly to the Battery Term post with a fuse as close as possible to battery.
For the Ground aka negative circuit conductor, locate the factory Battery Bonding Jumper to chassis. Cannot miss it, it is the cable on the Battery Negative Term Post. Typically bonded to Wheel Well, or Fire Wall. Remove factory bolt. Clean any paint, grease, dirt off and make sure you have bright shinny metal. Use an anti-oxidant. Place your radio negative cable Ring Terminal on TOP, not below Factory Rind Terminal. Replace factory bolt and Locking hardware. Same effect as directly to battery post with respect to low voltage loss, but takes your radio out of a Nasty Nasty Ground Loop. Anyone tells you different, tell them to pound rocks, they do not know what they are talking about.