A good, solid ground cable from the engine to the frame is essential to a properly functioning electrical system, especially with EFI. We fabricated a 2-gauge ground cable and covered it in harness tape and Mr. Gasket's G-Sleeve to match our fuel and coolant lines under the hood. | 
Once we reached the starter with the main battery cable, we cut the cable to length, added the terminal end, and covered the cable to match with more G-Sleeve. Notice our ground-cable installation from the starter-mounting bolt to the frame's engine-mount bracket. The bracket was cleaned of all powdercoating, and a mounting hole was drilled to attach the ground cable. | 
Due to the potential alternator output of our 150-amp Tuff Stuff Performance Products alternator, a typical 8-gauge charging wire isn't a safe application for our project, especially with its rear-mounted battery. Instead, we used a 4-gauge cable with a 200-amp Mega-Fuse for circuit protection. We mounted the fuse holder on the same frame member as the starter solenoid for easy servicing in the future. |
The rear body harness was routed through this precut hole in the driver-side, foot-box engine panel. We simply routed the wiring for fitment purposes. When all is said and done, there will be a protective strip on the edge of the aluminum, the wiring will be encased in plastic harness convolute, and wrapped in harness tape from RJM Injection Technologies ($3 a roll from the company's Web site). | 
The harness that carries the wiring circuits for the headlights, horns, electric fans, and so on passes through the front of the driver-side foot box at the top above the master cylinder. The opening is sized for the molded seal found on the wiring harness you would get as a donor part from a late-model Mustang. We "resized" the hole by placing a Seals-It firewall seal (PN GS404-16, $27) in the opening. | 
You can see the main spool here from the rear body harness before we routed it from the trans tunnel to the left and right corners of the chassis for rear lighting. It looks intimidating because of all the wires, but each is clearly labeled with its application, making it easy for even first-time "electricians" to wire their car. |
Once the wiring was routed and we were sure all circuits were covered (it's not a bad idea to add a couple of wires to the bundle now for future add-ons such as backup lights, a trunk light, a stereo, and so on), the wiring was encased in plastic convolute. We cut away the temporary tie-wraps as we moved along the length of the harness. | 
While FFR supplies a good amount of convolute in the kit, we ordered a Flexible Wiring Covering kit from Mr. Gasket (PN 4457, $23) for some additional convolute. The kit comes with several plastic Ts and inline outlets, as well as plenty of harness-mounting clips. The Ts and inline outlets come in handy for routing the wiring throughout the project while protecting the wiring. | 
A rivet (as shown here) or other fastener can secure the harness clips that come with the Mr. Gasket kit. These clips allow easy removal or repositioning of the harness for servicing or repairs. |