Where should the negative power return of a mobile transceiver be connected in a vehicle?
Why A mobile transceiver on transmit can draw 20 amps or more, and that current has to return to the battery through a low-resistance path. Running the negative lead directly to the battery's chassis ground point (or the battery negative terminal itself) gives a heavy, short return path, minimizing voltage drop at the radio and keeping alternator whine and other vehicle noise out of the audio. Both power leads, positive and negative, should be run as a pair straight to the battery and fused.
Watch out Grabbing any convenient metal part of the vehicle or using the mounting bracket seems easy, but modern car bodies have painted seams and thin sheet metal, so the return path has enough resistance to cause voltage sag and noise, and the current may wander through wiring harnesses it should not use.
Both power leads go to the battery, not to the nearest sheet metal.