Mystery cable under dash

[tucsonjwt]

When removing the HVAC duct under the dash of my 83 Chevy C20 to replace the heater core, I found a loose cable. It is 20" long with 3/4" brass fittings on each end. The brass ends are both squared off. One end was fitted into a plastic insert in the ash tray frame under the dash, the other end was loose (somewhere at or near the firewall?). (Photo attached, but not a good photo.)

Does anybody know what this cable is for? It has the number "2526" stenciled in white lettering on it.

On a side note, after I removed the cable I ran both of my dual tanks low so that I could add a fuel cleaner (per label instructions), and now my fuel gauge reads 1/4 full all the time, after I filled both tanks. Could the cable be related to this, or did I just kill the old sending units by running the tanks low?

Thanks.