Be real careful following schematics!!
All properly designed high resolution wide dynamic range or noise-critical circuits isolate power grounds that carry any significant current from signal grounds. They have to be wired in a particular fashion that may be different than it appears on a simple schematic.
A power ground and signal ground can be common at one point, but not at two points. Because of that, the common point connected wires might appear as a single wire in areas where they are really still two wires.
I hope this is understandable. I can give you a specific example in the 1989 Mustang negative battery connection. The negative post routing is heavy cable from battery terminal to the block, and a smaller wire from the battery terminal connector to the vehicle chassis. The smaller terminal wire is common at the ground lug with the injector and other very noisy grounds. The routing is critical for safety and noise mitigation, but it does not appear in the Ford OEM schematics exactly like wires really connect in the actual car. Look at what the Ford OEM schematic shows below for negative post. It is nothing like the actual battery negative wiring!!
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89 LX. 363, single turbo, Super Vic EFI, TFS high port heads by TEA, solid roller, glide. Holley HP EFI. (exact combo varies)