As part of some investigation into the systems of the house I live in, I was looking at the grounding and bonding wiring for the house, as most of it is accessible from the basement utility room.
In particular, I found that there is a bare 6AWG wire that runs from the casing of an abandoned-in-place well in a cellar-space under the back yard, up to the ceiling, through the back foundation wall alongside the old water line from the wellhead equipment (all of which was abandoned in place as well), along the utility room ceiling, and off into a finished ceiling space in the basement, but in the right direction to be connected to the panel, which is located in the garage. This wire is also connected through a tap splice of some sort to a second copper wire (which appears to be 10AWG or so?) that connects to a ground clamp on the cold water pipe system.
How can I verify that this wire is connected to what it appears to be connected to (aka the main panel in the garage)? I would like to use it as a place to tap retrofit equipment grounding conductors, as I should be able to reach down there from the range and especially the laundry equipment (dryer and washer) with relative ease, and there is also an improper (run to cold water pipe) retrofit ground wire on the furnace circuit that I would like to convert to a proper (albeit possibly redundant) retrofit ground wire.
Note that the furnace circuit is run in EMT for an unknown length, with metal boxes, so I do have effective access to both ends of that retrofit EGC. Also, the electrical panel is flushmounted into a finished garage wall, so I have no access to that end of the purported GEC.