No problem, I enjoy helping those willing to learn. To answer your question, if you were to flip your Underhood
Fuse block upside down, the part that connects the battery cable input to the fuses is referred to as the power bus.
What you are really looking for is something that you can easily touch with your voltmeter probe, so the "Aux A" and
Aux "B" connectors at the back are perfect for this IF the fuses feeding those are installed. I've modified the Bird's Eye
view of the fuse block to make this a little more clear:
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Fun fact - if you go back to the last wiring diagram, these 2 outboard power connections are referred to as 'Stud A' and 'Stud B'.
Notice that since my chore truck ('99 C2500) didn't come with any options (police, camper, etc) that would make use of these
outboard power studs , they didn't bother to populate those 2 fuse locations. However, on your vehicle if the fuses are in place then
just touch your voltmeter to one of these studs. If your truck is like mine, then while the truck is working correctly try and
probe where the circles are and 2 out of the 4 locations should reward you with a quick place to check the voltage in your
Underhood fuse block.
The idea is to find a place where you can easily compare the power in your fuse block (that feeds the entire vehicle) vs the
power right at your battery terminals. And all we're trying to do is figure out what's going on when everything goes out on
your truck right after attempting to crank the engine over.
Hope this cleared up any confusion. Happy hunting --