Suggestion… don’t remove/alter any of that original wiring… just tie it back using wire ties…..
Unless you are going to ‘show’ your Avanti and do it for esthetics, I believe you’re better off leaving it all intact….
Just unplug and remove the electronic control module….and either manually (or through the use of the many aftermarket kits available) activate your lockup torque converter.
I did the above when eliminating electronic engine controls on my own ‘83 Avanti, which I use for everyday transportation, many years ago… and have had no problems whatsoever!
(also…remove the fuse at fuse box sending power to the ECM…. and, of course, you will need a non electronic controlled distributor and carburetor)