name that wire! 1965 c10

[kljfamily]

Hi, 1965 c10 250

Can someone tell me where this wire goes?

It is a thick black wire that comes out the drivers side firewall next to the wiring harness plug but not a part of it. It has a hard plastc shell under the black and a copper wire. Its right next the the throttle cable. In the pic its one of the two Im pointing towards with he cable end.

Thanks

i have the wiring diagram but cant figure this one out.