Connectors Under Dash

I can tell you how I do it, doesn't mean mine is the only way...
First I unscrew the sheathe collector nut from the trans and point it to a shop towel.
Then I go in the cab and pull the cable from the sheathe. Then I flush the cable and the sheathe interior first with brake cleaner then with compressed air. Then I take a tub of white lithium grease to the floor board and grease the cable between my fingers while shoving it back into the sheathe. Reattach sheathe at trans. Use Q-tip to remove excess grease inside instrument connector. Reattach to instrument.