About once a year I get all spun up regarding this issue. Grounding a mobile radio. If you get QST you may have seen an article in the May issue on page 35 about this issue. It set me off again. “Oh my goodness, new electronics systems in a car mean we have to change the rules on how we ground our radios!” Here’s the deal, if hams were doing it right all along, there would be no need to make a reactionary change in order to not screw up the electronics on your new car.
The new battery monitoring control circuitry proves that automobiles are designed to use a chassis ground. If all these chassis grounding failure modes are so common than why are there not 200 ground wires run to a battery from the factory??? the electronics on board automobiles even since the mid 90’s are very advanced when compared to the circuitry in your typical 2m mobile rig. The manufacturers and their vast engineering teams even use chassis ground as a reference point for high precision sensors and data bus systems. It’s how it in done in a car. You’re putting your radio in a car, follow the automotive industry standard practices and you will not have problems. That means any electronic device installed in a car should have a local grounding point as close as possible. Thats how the 15 computers and hundreds of loads on any car in the world are designed. And thats how added in electronic components should be connected as well, even your radio.
Well, when the manufacturers (automobile and amateur radio) specify to connect positive and negative direct to the battery, people will tend to do that. Before load monitoring in the vehicle negative lead became common, potential voltage drop under high currents as well as elimination of noise from possible ground loops were the driving reasons for doing so. See http://www.k0bg.com/wiring.html for a detailed discussion on the topic.
I agree that ground loops can be a big factor to fight with. Using a single star point as a kind of intersystem or interdevice bonding point may be helpful to avoid such grounding loops. Haing a direct connection to the chassis ground or to battery ground from such a star point should cut down on interference as well. Keeping the grounding runs to a minimum required length would also be a good idea so as to un-invite any potential intruders.