engine to firewall ground wire
Ford had three different engine-to-firewall ground wires, as shown here:
The 80/83 version is typically a braided and un-insulated wire, but note that there is no part # shown for it and the instructions are to improvise by using #8 wire and eyelet terminals, and that # translates to "Eyelet - No. 10 stud - for No. 8 gauge wire".
The 84/86 version is part # E4TZ 14303-A and is marked E4TB 14303-AA as shown below (thanks, Rick), and includes a connector that goes to the Electronic Control Assembly (ECA) that is used on some trucks. If yours doesn't have an ECA that connector is not used.
As for where it connects on the engine, here's what the 1986 EVTM shows, and it is G208:
And, here's what it shows for where it goes on the firewall, and that end is G710: