I followed the instructions included by the radio manufacturer, which called for connecting the negative lead directly to the battery.
Like I said do not take any ham radio operator advice installing radios in a vehicle. They know nothing of vehicle electrical systems. Taking the negative directly to the battery term post is extremely dangerous. If you ever bothered to look at the circuit would quickly realize you just put their radio Negative return wire and coax shield in parallel with the vehicle negative bonding jumper. That means a portion of all vehicle current, including cranking current, is flowing on your coax shield and radio negative lead. All that outside vehicle current flowing through your radio is common-mode noise. One of them is alternator whine on TX audio, or the pops and clicks as thing cycle one and off.
Real surprise comes if you have a mechanic work on the battery and forgets to reconnect the vehicle bonding jumper to the chassis, or it gets damaged. You will never know it until you go to start the vehicle. You put the key in the ignition, all the bells, lights, and whistles come on normally, you turn the key, and the cab fills up with smoke. After you put the fire out and investigate, you find your coax shield, radio DC negative wire, and circuit boards burnt to a crisp smart guy.
Try a little experiment. Get a DC clamp-on amp meter and clamp it to your radio DC negative and monitor it.
Turn off your radio. Now insert the key and crank the engine while observing the amp meter. Please explain why you see 5 to 10 amps of engine cranking current flowing through your radio. After the engine starts, turn on all your vehicle electrical accessories. Turn on the AM/FM to ghetto sound level, high beams, roll the electric windows up and down and seats back and fort, then comeback and explain why you have vehicle currents flowing through your radio system. You are in a nasty ground loop, and hams love to be in Ground Loops.