· Super Moderator
Certainly. The main ground cable goes to the engine block, to ground the starter and other electronics mounted on the engine. But other electronics, such as gauges, computer, stereo, etc, ground to the chassis (firewall, dash, body panels). The engine is electrically isolated from the frame at the engine mounts, and only has a casual electrical connection from wherever the transmission and axle touch the frame in any way. The resistance there can be several ohms. Therefore, there is also a ground wire from battery to frame/fenderwell/bulkhead. Without that ground connection, any ground return from the chassis/dash, etc. has several ohms of resistance between it and the engine ground. Therefore, those grounds are not at zero volts, but at some higher voltage as determined by the resistance. Therefore, you have devices running inside at somewhat less than 12V, and you have a ground loop, or current, flowing between the virtual grounds of the interior and the engine ground.