Negative chassis ground location

[fremont]

I can see two negative wires coming off battery terminal towards frame.  I'm assuming large negative goes to bolt on frame; where does smaller negative go?

[Snowcamo]

The body. Its right there. Follow it and it goes straight to the cab.

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[fremont]

I'm trying to hook up a VHF/UHF radio using this diagram.  Does an '18 Silverado have a battery power monitoring feature (same as "ELD" in diagram)?  I know I've got a voltage meter but unclear how it hooks up or whether it's synonymous with what the diagram calls ELD.