Under dash wiring connectors

It is a PITA, but I've used a .22 bore brush, a Dremel tool with a wire brush, contact cleaner, and a jeweler's screw driver to clean up an underdash wiring harness. Also cleaned up the big plug in the firewall that it all plugs into.

I found it easier to remove the harness to do the work. Besides that it also made it easier to "ring out" the harness and make sure there were no breaks or "cross-talk" between the wires. FWIW: It took me three weekends working up to 7 hours a day.