the wire is not factory, so it's impossible to tell where it originally went. could be from a previous hack that was removed, or from a repaired factory wire that was bypassed... finding the other end if it's still there would be more helpful.

I have never had my reservoir removed on any of my cars, so I'm no help on that end... sorry. the foot does look like it goes on the bulb on the bottom of the reservoir though.
is your reservoir mounted to the front radiator support with a metal cover over it or attached to the fenderwell?

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!