Grounding Windlass Solenoid

[Amwasp]

I could use some electrical advice.
I just replaced a solenoid on an old Lofrans Windless. Attached is a sketch of the wiring as I currently have it. It works fine but:
There was an additional wire (12 gauge) that was crudely attached to the Main Ground wire on the Windless (dotted line). I checked the 12 gauge line with a meter while detached from the terminal by putting one probe on the ground terminal and one on the 12 gauge. it shows no resistance. Also when I put a lead on the hot terminal and one on the 12 gauge I get no voltage. This tells me that it is not a ground wire and serves no purpose.
Questions:
1)Is my assumption in the ballpark?
2)Should the windless system have a secondary ground and where should it be connected?
3)What are the possibilities as to what the 12 Gauge wire is? A ground wire gone bad? A jury rigged ground for another device?
Oh yeah, this is a single direction windless.
Thanks

[Paul L]

Is there no ground on the solenoid? It is just a relay and needs + and -.

Paul L

[donradcliffe]

when you say 'no resistance' to the ground wire, do you really mean 'infinite resistance' (no connection) or 'zero ohms' (good connection) ??

[GordMay]

The (large?) Wire that you’ve labelled Ground (-) is the 12VDC Negative Power return. Although the DC Negative is grounded, it shouldn’t be called a ground wire.
The (dotted?) #12 wire may have been a bonding cable, intended to go to the ground bus.

[Amwasp]

Thank you all.
I tracked down the 12 gage wire and found that it is a ground wire for the solenoid as Gord said. The wire is broken so I'll have to pull another through the bulkheads. Just got a wiring diagram from a tech guy that sold me the solenoid. I attached it for posterity sake. Also added the wiring diagram for two direction wiring.
When I said resistence, I used the wrong term. I meant to describe tthe condition of infinite resistance.
Thanks again.