A number of people have asked me, via PM's, how to wire a Mod Motor into a Fox body. I don't claim to be an expert but if it's of any help to anyone, I'll try to pass along some of the things I learned from experience.
Fuel injected Foxes have a pretty much separate wiring harness for the computer. The big difference in the SN-95 Mustangs with Mod Motors is the computer wiring is integrated with the rest of the wiring in the engine compartment. The Mod Motor has 5 wiring harnesses under the hood. There are two on the engine, the engine harness (P/N 12B637) and the starter harness (P/N 12A690). The computer harness (P/N 12A581) is on the right side of the car, and the fuse box harness (P/N 14290) is on the left. The transmission harness (P/N 15525) plugs into the computer harness.
The starter harness has the battery terminals, connecting to the battery mounted left front. The starter harness connects to the fuse box harness thru two connectors (#112 and 113) and with a cable to the stud on the fuse box. The starter harness also connects to the engine harness thru an 8-pin connector (#1005). The fuse box harness connects to the engine harness thru a two pin connector (#100) and a fuse link to the stud on the fuse box. The fuse box harness also connects to the computer harness thru a 16-pin connector (#108) and a 4-pin connector (#109) both behind the right headlight. The computer harness connects to the engine harness with two connectors, a 40-pin (#104) and a 4-pin (#101). The computer harness has 4 connectors (#202, 213, 216, and 259), and the fuse box harness has two connectors, a 24-pin (#105) and a 16-pin (#107), all six of which eventually connect to the dashboard. The attached sketch below of the harness interfaces spells it out more clearly. Everything to the left of the vertical dashed line is in the engine compartment, and everything to the right, the main harness and instrument panel harness, are unique to SN-95's and don't apply to Fox body cars.
If you're putting a Mod Motor in an injected Fox, what you need to do is break into the bundle of about 40 wires that comes from the dashboard and thru the firewall with a big rubber grommet. A non-injected Fox is somewhat different because the battery is on the right and there is one harness that forms a large "U", connecting at the center to the dashboard wiring, and both ends coming down opposite sides of the engine compartment. I recommend mounting the battery on the left (or in the trunk, an easy modification), using the Mod Motor starter harness, keeping as much of your Fox wiring as possible, and removing what you don't need (lights, windshield washer, ABS, air bags, etc) from the Modular computer and fuse box harnesses. The fun part will be matching the wires coming out of your dash to what's left of the Modular harnesses. It's not difficult, just tedious, and the best investment I made besides the wiring diagrams for both the donor and receiver cars was a $15 multi-meter from Radio Shack.
There are a few differences worth noting. On Foxes, the fuel pump relay is near the tank while on SN-95's, the relay is in the kick panel on the passenger side and plugs into the computer harness. Bypass the trunk-mounted relay and use the one on the Modular computer harness. Much easier that way. Also on the computer harness under the right front fender are a fuel pump resistor (it's made of white clay or porcelain and looks like something from the '20's) and the Constant Control Relay Module. You need both to make the Mod Motor run. If you're going to have cruise control, grab the Modular electronic unit from under the left front fender. The cruise control from a Fox is a real Rube Goldberg device that used vacuum diaphragms, resistors, chain linkage, and other strange stuff. The electronic unit is more reliable and can be connected using the wiring that goes to the relay boxes under the Fox dash.
I've counted about 16 different combinations of Mod Motors/transmissions and Fox body cars, even without counting Mark VIII's or 3-valve Mod Motors. I don't know the specifics of every possible combination but I hope what I've written here will be a starting point.
Good luck with your conversion!
Fuel injected Foxes have a pretty much separate wiring harness for the computer. The big difference in the SN-95 Mustangs with Mod Motors is the computer wiring is integrated with the rest of the wiring in the engine compartment. The Mod Motor has 5 wiring harnesses under the hood. There are two on the engine, the engine harness (P/N 12B637) and the starter harness (P/N 12A690). The computer harness (P/N 12A581) is on the right side of the car, and the fuse box harness (P/N 14290) is on the left. The transmission harness (P/N 15525) plugs into the computer harness.
The starter harness has the battery terminals, connecting to the battery mounted left front. The starter harness connects to the fuse box harness thru two connectors (#112 and 113) and with a cable to the stud on the fuse box. The starter harness also connects to the engine harness thru an 8-pin connector (#1005). The fuse box harness connects to the engine harness thru a two pin connector (#100) and a fuse link to the stud on the fuse box. The fuse box harness also connects to the computer harness thru a 16-pin connector (#108) and a 4-pin connector (#109) both behind the right headlight. The computer harness connects to the engine harness with two connectors, a 40-pin (#104) and a 4-pin (#101). The computer harness has 4 connectors (#202, 213, 216, and 259), and the fuse box harness has two connectors, a 24-pin (#105) and a 16-pin (#107), all six of which eventually connect to the dashboard. The attached sketch below of the harness interfaces spells it out more clearly. Everything to the left of the vertical dashed line is in the engine compartment, and everything to the right, the main harness and instrument panel harness, are unique to SN-95's and don't apply to Fox body cars.
If you're putting a Mod Motor in an injected Fox, what you need to do is break into the bundle of about 40 wires that comes from the dashboard and thru the firewall with a big rubber grommet. A non-injected Fox is somewhat different because the battery is on the right and there is one harness that forms a large "U", connecting at the center to the dashboard wiring, and both ends coming down opposite sides of the engine compartment. I recommend mounting the battery on the left (or in the trunk, an easy modification), using the Mod Motor starter harness, keeping as much of your Fox wiring as possible, and removing what you don't need (lights, windshield washer, ABS, air bags, etc) from the Modular computer and fuse box harnesses. The fun part will be matching the wires coming out of your dash to what's left of the Modular harnesses. It's not difficult, just tedious, and the best investment I made besides the wiring diagrams for both the donor and receiver cars was a $15 multi-meter from Radio Shack.
There are a few differences worth noting. On Foxes, the fuel pump relay is near the tank while on SN-95's, the relay is in the kick panel on the passenger side and plugs into the computer harness. Bypass the trunk-mounted relay and use the one on the Modular computer harness. Much easier that way. Also on the computer harness under the right front fender are a fuel pump resistor (it's made of white clay or porcelain and looks like something from the '20's) and the Constant Control Relay Module. You need both to make the Mod Motor run. If you're going to have cruise control, grab the Modular electronic unit from under the left front fender. The cruise control from a Fox is a real Rube Goldberg device that used vacuum diaphragms, resistors, chain linkage, and other strange stuff. The electronic unit is more reliable and can be connected using the wiring that goes to the relay boxes under the Fox dash.
I've counted about 16 different combinations of Mod Motors/transmissions and Fox body cars, even without counting Mark VIII's or 3-valve Mod Motors. I don't know the specifics of every possible combination but I hope what I've written here will be a starting point.
Good luck with your conversion!