For troubleshooting, generally one looks at the battery as the starting point, not some other connection.
Incase it is not crystal-clear.... the REASON the battery-minus post is considered the 'beginning' of all circuits on the machine is because this is where the electrons themselves originate. (current flows from minus-to-plus)
The description some folks giving for the engine-case (frame) as the 'origination' is due to what is known as a "mecca ground". In circuit-design, A "mecca ground" is considered the node where all the current terminates.
Properly designed automotive circuits will rarely rely on the engine-case (frame) as a current-carrying component. This is because the current from EACH AND ALL of the circuits will be additive.
Some older machines may use one-wire sensors on the engine. (oil-pressure, water-temp....etc) This is a rare example of using the engine-case to carry current.
It is
VERY poor wiring-practice to 'just hook to the frame' when one needs a ground. Suddenly, current is flowing thru metal which is NOT intended to carry current. It is FARRR better to always use engine-case as the "mecca ground"...and have a VERY heavy wire from engine-case to battery-minus. Even better, all the wires connected to the engine-case should be underneath the SAME BOLT on the engine-case.
I have personally troubleshot and diagnosed strange electrical problems such as "
charging current from alternator passing through BEARINGS because engine-case was not connected to battery-minus" The only place the current could flow from alternator-minus was thru rotating engine-bearings to get back to the battery-minus.