You are totally right with these examples, I must admit, Russell!

That's a typical discussion which I don't like very much: We don't know anything about the concrete setup but try to improve the situation, each one from his own point-of-view.

Let's recall what we know: Mahmood wants to totally isolate the chassis from the electric of car, because he thinks, that the chassis, as ground plane, will rather act as an unsane antenna injecting noise into sensible equipement, than as a helpful shield.

Ok, I say, keep the awful heavy currents isolated from the chassis, by routing the according ground return currents directly to the minus pole of battery. This you can do with the grounds of generator, starter and eventual ventilation motors.

But then, connect the chassis to the minus pole of battery and use the chassis as reference plane for all the other electronic circuitry, assuming, that the associated ground return currents running through the chassis are only small. I think here of decentral board computers, navigation systems, sensors, distance warners, small lamps, door locks, etc. etc., means all that stuff, that has to do with communication and sensoring but not with controlling of huge currents.
In this case I suggest to use shielded cables with the shield connected to the chassis at both ends and routing these cables in close distance to the chassis plane in order to minimize loop areas.

If additional high current applications are to handle in this car, then I would locate the according power control units near the battery and route all the associated ground return currents (assumed to be huge again!) via separate cables, means isolated from the chassis, to the minus pole of battery. If there are sensors mounted near the high current applications, think of something located in the rear of the car, then these can still be referenced with the cables shields to the chassis plane. Here the ground plane performance can help to minimize the inductivity of these sensors cables, which would make them otherwise antennas eventually picking up short wavelength radiation.

There are several sensors in a car, where the signal is only changing very slowly. These don't necessarily need shielded cables with the shield connected at both ends to the chassis. Here a suited low pass filter can also suppress noise and interference. The double connecting of shields is more recommended on higher speed data communication, where no simple low pass filters can be used to suppress interference, and where the single side connected shield would result in more interference than a double side connected one.

All the electronic communication should be done by using symmetrical signal routing or "differential communication" respectively, as Erik mentioned, in order to suppress any unavoidable common mode noise.

What do you think about this concept?

Kai