Amateur (ham) radio installation - 2011 A3 TDI

[Bill1975]

I've been a licensed amateur radio operator for a long time, but have recently been interested in installing a mobile transceiver in my car. The radio I'm considering (http://www.icomamerica.com/en/products/amateur/mobile/id5100a/default.aspx) requires 12 volts and draws 13 amps at maximum power. What confuses me is whether I should connect the negative lead directly to the negative battery terminal, or a nearby chassis ground point. The prevailing wisdom is to connect to the chassis and not to the negative terminal due to potential problems in case of a ground fault, and also any onboard sensors monitoring battery usage. However, looking at the factory repair information (see pics) it suggests I should connect directly to the battery, as well as a third wire (that doesn't exist on any wiring connector for any mobile radio I've seen) going to "terminal 15a". I'm not sure what or where that is. The radio's manual seems to suggest it's fine to go directly to the terminal as well (the radio comes with a power cord that is fused on both wires).

So 1) Negative terminal or chassis ground? and 2) What is terminal 15a and how important is it?

https://i.imgur.com/OZGWLMC.jpg

https://i.imgur.com/oL9gk7d.jpg

[Bobby Kinstle]

Negative terminal to chassis, and you might need an alternator noise filter if you hear a whine that follows engine speed.

[Bill1975]

Another vote for chassis ground, thanks!