Not sure what's up with the photo not linking. I use Photobucket as well. However, from your description I know what wire you are asking about.
The small, loose purple wire in question is the jumper wire that the installation manual mentions to use in the ICM connector:
What you do not see in the photo is the splice to connect that jumper wire to wire number 18 from the OEM computer harness.
Question now is - do you have an HEI setup? If so, you don't need the jumper wire because the HEI takes the place of the factory ICM. If you don't have HEI then you should have the following:
It's basically the Nutter Bypass but Howell gives you a weatherpack pin/jumper wire to make use of the open slot in the ICM connector. Lets you easily disconnect the ICM to replace it, without having to cut wires.