In building a replica, do we need to feel as though we’re masters of all the automotive trades, or maybe specialists with great expertise for just specific portions of the build? In other words, are we wimping out if we skip some build aspects where we don’t feel that we’re automotive gurus in certain disciplines? I suppose that depends upon your point of view.
This Tech Tip is From the Full Book, HOW TO BUILD COBRA KIT CARS + BUYING USED. For a comprehensive guide on this entire subject you can visit this link:
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Our objective all along was to build the best possible FFR Mk4 Cobra roadster replica, and building this industry-leading kit car is similar to building other Cobra replicas. Mind you, if we have a deficit in our abilities, we’re not going to jeopardize this overarching goal out of stubbornness. We bring in the experts when we know they can do a better job than we can.
When it came time to wire our sexy roadster, we followed the FFR Mk4 Complete Kit manual to the letter because an improperly installed wiring harness can be dangerous and even result in a fire. The manual recommends reading the Factory Five/Ron Francis Chassis Wiring Harness Installation Instructions before tackling the car’s wiring. We dutifully immersed ourselves in this manual. It’s well written, provides sharp color photos, and has a thorough wiring schematic. We felt confident that, with sufficient time and a fair amount of troubleshooting, we could indeed tackle this daunting wiring task.
But did we want to do it? After careful consideration and contact with our new friend Dennis Clark, owner of Carlsbad Automotive Technology, we decided that we’d rather rely on a professional automotive electrician than on our stubborn persistence and great enthusiasm for the electrical puzzle before us.
If you have experience in automobile electrical wiring, you’ll be able to accomplish a great wiring job on your Cobra replica with all the information here, your manual, and what you already know.
Beyond that, if you ever decide to put your Cobra up for sale, a highquality wiring job is readily apparent to the trained eye. A knowledgeable potential buyer recognizes sound wiring connections, correct material use, correct termination points, wisely routed wires, and properly mounted fuse boxes.
Project 1: Wiring Harness and Fuse Box Installation
Step 1: Inspect Components
The Ron Francis Wiring Kit supplied in the FFR Mk4 Complete Kit is first class all the way. You get the dash harness, main harness complete with fuse box, front harness, and the rear harness. Just supply some brainpower and common sense, in addition to the following tools: wire crimp tool, rivet gun, tin snips, cordless drill, 1¼-inch hole saw, 5/16-inch drill bit, wire cutters, 5/8-inch hex key, 1/4-inch nut driver, 3/8-inch wrench, and 7/16-inch wrench. With the instruments that you order from FFR in the Complete Kit Mk4, you receive an instrument harness that is specifically for the gauges you select, in addition to the oil pressure sensor and coolant temperature sensor.
Step 2: Mount Fuse Box
The fuse box is attached to the main harness. To begin your electrical odyssey, attach the fuse panel to the fuse panel mount using the FFR-supplied 1/4-inch screws and locknuts.
Step 3: Install Fuse Box
Use the number-6 self-tapping screws to install the fuse box to the 2 x 2-inch frame tube and the 3/4-inch tube. Drill holes in the frame tubes with a 1/8- inch drill bit. The fuse box is positioned above the driver’s left leg in the pedal box. The fuse panel hangs upside down in the top portion of the left side of the footbox, so that you can maintain access and change blown fuses.
Step 4: Fabricate Shielding Shelf
For now, lay the main harness conduit over the steering shaft. The dash connectors and ignition switch wires need to be temporarily pulled into the cockpit area so they are kept out of the way during the installation. At this point, fabricate an aluminum platform that arches over the steering shaft and its bearing to shield the main harness from the rotating steering shaft. Use tin snips to cut the panel out of some extra aluminum. Then bend the aluminum around your workbench vise to approximate the shape of the steering shaft bearing. Drill holes in the panel and use those panel holes to drill holes in the frame tube that the steering shaft bearing and steering shaft are attached to. We rivet the panel in place. Install the shelf with self-tapping sheet-metal screws or rivets and run the wiper/radio harness wires toward the passenger’s side along the top of the 2 x 2-inch cockpit tube.
Step 5: Attach Ground Wire for Fuse Panel
Thoroughly grind off all the powdercoat on the 3/4-inch tube where you install the fuse panel’s ground wire. You need metal-to-metal contact between the connector and the chassis to have a consistent and reliable ground. Having a well-grounded electrical system in an automobile is crucial, but especially in a fiberglass kit car. Whenever you’re attaching a ground wire, make sure to remove all the powdercoat at the spot before installing it.
Step 6: Install Brake Switch Connector
Remove the plug from the brake switch wire and install the brake switch spade connectors into the brake switch. If the spade connectors are damaged by removing the plug from the brake switch wire, re-crimp these spade connectors to the appropriate wires. We did not have this difficulty, so we could simply plug the connectors into the brake switch.
Step 7: Solder Clutch Safety Switch
When you attach the clutch safety switch, the car doesn’t start if it’s in gear. If you opt to not use this, connect the two wires and either terminate them with an FFRsupplied butt connector, or solder them together and insulate them with electrical tape. We chose to solder ours.
Step 8: Plug In Sending Unit Connector
Find the FFR-supplied gauge-sending-unit wire harness and plug it into the sending unit connector on the main harness. The plug is a male/female setup and is brown in color.
Step 9: Enlarge Hole for Electrical Conduits
Because some of the electrical conduits need to be run to the engine bay, open up the hole to the right of the driver’s knee in the top corner of the pedal box. We opened our hole up with an electric drill and deburring bit. The starter/coil harness and the rear harness can be routed through this hole. Factory Five Racing also supplies some clear plastic trim to install on the rough edges to smooth these edges and prevent tears in the electrical conduit. This is a crucial step in preventing any potential wire damage. Also file the edges smooth, as we’ve done.
Step 10: Route Front Wiring Harness
There’s a large hole in the top of the front driverside footbox wall, directly under where the front brake line is run. Route the front harness through this hole. Use a hole saw and an FFR-supplied block-off plate to drill the correct-size hole. Use a 1¼-inch hole saw.
Step 11:Install Conduit Hole
By clamping the donut to the front of the footbox, you can drill rivet holes in the aluminum conduit grommet. After these holes are all drilled, apply silicone to the backside of the doughnut before mounting it with a rivet gun and rivets.
Step 12:Install Alternator Conduit and Ground
The Ron Francis Wiring Instruction Manual, supplied with the FFR Mk4 Roadster Complete Kit, recommends routing the alternator and gauge sender wires through the hole that we (and perhaps you) enlarged in the top-right corner of the driver’s footbox. But that hole still isn’t really large enough to accommodate all the conduits that are supposed to be routed there, so we opted to drill one hole in the passenger-side firewall to send the alternator wires through. If you follow our lead, use a 1¼-inch hole saw and cordless drill to put a hole in the passenger-side firewall. Have your build partner hold a block of wood behind the aluminum panel where you’re drilling. That aluminum cuts fast, and you have a better solution than stuffing a bunch of electrical conduits into one hole. The alternator also has a ground wire, which we’ve grounded as shown. We used a rubber grommet, from a local auto parts store, to protect the plastic conduit that houses the alternator wires. We also soldered on a ground eyelet and shrink-wrapped the wire. FFR supplies many of these little ground eyelets in the kit.
Step 13: Attach Wires to Alternator
If you route the alternator wires in a similar manner, strap the alternator conduit (with the FFR-supplied line clamps) to the passenger-side, top engine bay tube that frames the hood and the front of the car. On our Powermaster high-performance one-wire alternator there isn’t a ground terminal, so we grounded the negative wire to the alternator’s case (as shown) and installed the positive power wire to the one-wire terminal. We cut off the modern alternator plug that was on the end of this harness and soldered on an eyelet, which is compatible with our Powermaster alternator. We also soldered on a ground eyelet for the negative terminal. Installing the alternator wires like this goes a long way in creating a sanitary engine bay.
Step 14: Install Fuel Inertia Cut-off Switch
An easy thing to do is to install a fuel inertia cut-off switch. Locate it on the front or back of the 2- x 2-inch tube; be sure not to cover the stamped chassis numbers. Use the supplied number-8 self-tapping screws, an electric drill, and a 1/4-inch nut driver. Also, the red switch needs to be in the upright position, as shown.
Step 15: Route Rear Harness
Find the rear harness in the wiring box and connect it to the connector on the main harness. The two plugs should be obvious. Run the rear harness through the enlarged footbox hole and through the transmission tunnel. Securely zip-tie the rear harness so that the conduit doesn’t interfere with the driveshaft.
Step 16: Plug In Rear Harness
Once the rear harness is successfully routed to the fuel tank, it’s time to plug in the sending unit and the fuel pump. Safely and securely tie this harness to the frame tubes so it’s out of the way of where the aluminum trunk floor is installed.
Step 17: Install Front Harness
Remember that aluminum conduit grommet you drilled out and riveted in place in the footbox front wall? There’s no time like the present to plug the front harness into the main harness. It’s a black male/female plug, and both harnesses are clearly labeled. The front harness is for the headlights, the low and high horns, and the electric fan. All of these electrical components will be hooked up later, so just drape the front harness over the driver-side hood-opening rail for now.
Step 18: Route Front Harness through Footbox Wall
From the front of the footbox wall, here’s how the front harness looks routed through the aluminum conduit grommet.
Step 19: Install Power Distribution Block
Our little high-torque Powermaster starter has a built-in solenoid switch. Factory Five Racing supplies an old-style Ford solenoid switch and a starter loom that has a plug on the end of the loom. To install this harness, FFR recommends you use a power distribution block (PDB) to achieve a clean installation. In this starter loom, there are three positive cables and a separate wire for the solenoid. The three positive cables are on the right and connect to each other via a copper strip. The solenoid wire is on the single connector. Other positive cables can be installed on the three positive terminals. You then can run a single positive power cable to the starter.
Step 20: Wire Starter
The wrapped positive-conduit cable atop the starter is the battery’s positive wire. The other conduit that circles below the starter is a short positive cable from the PDB. Inside the black conduit is the separate wire that we attached to the solenoid, which also runs from the lone solenoid terminal on the PDB.
Step 21: Install Ground Strap
Before attaching the engine ground strap to the engine, thoroughly grind off the powdercoat on the chassis where the strap installs, which is located on the passenger-side engine-mount frame. On an FFR Mk4 roadster chassis, the strap is attached on the engine mount frame on the passenger’s side. In fact, there is already a hole to accommodate the bolt and nut that holds the strap to the frame.
Project 2: Trunk Wall Installation
Step 1: Apply Silicone to Trunk Wall
Before you can install the battery, there needs to be a trunk; the battery goes in the trunk. With Sharkhide protectant applied to the inside trunk wall, put silicone on the backside and rivet this wall in place. There is no battery tray included in the kit. Your battery is located on the top trunk floor, unless you prefer some other location.
Step 2: Install Upper Trunk Wall
Apply silicone to the frame where the aluminum panels rest on the frame. This ensures that you’ve sufficiently sealed off the trunk from the elements and eliminate the potential for metal-on-metal squeaks or rattles. Once you have each panel held in place with a pick or two and some sheet-metal screws, rivet the panels into their new home.
Step 3: Install Fuel Tank Trunk Floor
Rivet the top of the fuel-tank trunk floor in place. After sanding, apply Sharkhide on the front side and silicone on the bottom side.
Step 4: Install Lower Trunk Floor
After some adroit application of Sharkhide protectant, drying time, and applying the silicone between the frame tubes and the aluminum, install the lower trunk floor.
Step 5: Remove Aluminum for Fuel Tank Strap
The passenger-side fuel-tank strap is routed through that side’s lower trunk floor. To accommodate the strap, remove a rectangle of aluminum in the panel with tin snips.
Step 6: Install Lower Trunk Floor
Repeat the easy process of Sharkhiding, siliconing, and riveting-in the various lower-trunk floor and wall aluminum panels; do not bury the license-plate light loom.
Step 7: Install License-Plate Loom
For the licenseplate loom, drill through the passenger-side lower-trunk triangular wall and use a grommet or the clear plastic around the hole, so that the loom’s conduit doesn’t rip. Run the license-plate wire just under the middle of the decklid (trunk) and zip-tie it to the center tube beneath the trunk. Keep it clean.
Step 8: Install Upper Trunk Floor
Now that the upper trunk floor has been installed, our Optima battery is placed amid all that sanded and Sharkhide-protected aluminum.
Project 3: Battery Installation
Step 1: Inspect Components
For our Optima battery installation, we used: the FFR-supplied battery hold-down brackets and locknuts; electric drill; a 1-inch hole saw; 3/16-, 1/4-, 5/16- inch drill bits; rivet gun, Sharpie marker, 7/16-inch deep socket; ratchet; 1/2-inch wrench; 3/16-inch hex key; the dry cell deep-cycle Optima battery; the positive battery cable; and the ground strap.
Step 2: Drill Holes in Trunk Floor for Battery
The recommended installation location for a battery in an FFR Mk4 Cobra roadster is the upper trunk floor near the wall that separates the cockpit from the trunk. FFR provides an 8-foot battery cable, so you have plenty of length for various mounting locations, including under the trunk. We have an independent rear suspension, so we decided to go with FFR’s recommendation and put our battery right where they think it’s best. Place the battery where you want it and mark where the holes need to be drilled for the two J-hook fasteners and for the battery cable and ground strap (negative battery cable). Then remove the battery. Drill the 1/4-inch J-hook holes first. Put the battery back in place and confirm these fresh holes are in the correct location for strapping down the battery. Also re-check the locations marked to drill, and install the positive and negative cables. Put the battery somewhere safe and get busy with your electric drill and 1-inch hole saw. The J-hooks hold the Optima battery in quite well. Notice the ground strap hole is in the foreground. The dead giveaway is the fact that we have no powdercoat on the frame that’s framed by the 1-inch aluminum hole we recently cut. Make sure you remove all the powdercoat/paint before you install the ground strap. If you’re building an FFR Cobra, you notice that the positive battery cable is pre-made and the same applies for the negative strap. However, the positive cable is 10 feet long and likely needs to be shortened. We opted to install both cables on the side terminals for easier access, since we had to shorten the positive cable anyway.
Step 3: Route Battery Cables
With the battery in place, route the battery cable through the hole in the floor and install the FFR-supplied rubber grommet. Attaching the ground strap is a snap. Using a lock washer and Loctite is highly recommended. Don’t attach the positive cable to the terminal yet. Remember, the electrical system isn’t finished.
Step 4: Install Fuel-Injection ECU
We determined where to install our Holley Avenger EFI ECU. Before installing, we made a template so we could drill the four attachment holes in an aluminum panel.
Step 5: Install Fuel-Injection ECU (Continued)
The FFR Mk4 Complete Kit manual recommends installing the EFI ECU on top of the passenger-side footbox in the engine bay, behind the dash on the passenger’s side, or on the ceiling of the passenger-side footbox. We selected inside the transmission tunnel on the driver’s side. We preferred this location for a couple reasons: the ECU is more out of the way here, and it uses up more of the harness length. Whichever location you choose, use rubber grommets and 1-inch stainless-steel “stilts” to counterbalance any chance that the ECU might succumb to vibration. Also use lock washers, Loctite, and stainless bolts and nuts with the stilts and the rubber grommets to keep the brain intact.
Project 4: Gauge Installation
Step 1: Inspect Components
Before we can get started on the electrical system, we need to install the gauges in the dash. However, we first need to make the dash. With an FFR Mk4 Complete Kit, the dashboard is foam-backed, vinyl-covered aluminum. Here are the gauges for the dashboard.
Step 2: Enlarge Tachometer and Speedometer Holes
If you have the same gauges we selected with our FFR Mk4 roadster, trim the tachometer and speedometer openings to accommodate the larger-style classic instruments. Use tin snips to cut along the pre-perforated, larger-diameter opening. Your manufacturer’s kit may have the same sort of arrangement. Thankfully, all the holes are pre-drilled. It’s easy to cut out the larger opening if you work carefully.
Step 3: Enlarge Holes with Rotary Tool
After cutting the opening to the larger diameter, you can use a round file or a Dremel tool with the round sander attachment to smooth the rough-cut edges.
Step 4: Glue Vinyl to Dashboard
Glue the foam-backed black vinyl onto the front of the aluminum dashboard. Use 3M Super 77 spray-on adhesive. Also put some heavy objects on top of the aluminum to make sure the glue fastens the foam to the aluminum. To be safe, let the dash sit in this state for a couple days to thoroughly dry before performing the next operations. You see those black lines all around the edges? Cut Vs all around, about 1/2 inch to 1 inch apart. Then apply adhesive and fold down the edges. Place heavy objects all around the border and let the glue thoroughly dry.
Step 5: Install Gauges in Dashboard
After cutting holes in the vinyl dash pad where the gauges go and making a plus sign where the steering shaft pokes through, carefully place the gauges into slots in their designated area. The tachometer and speedometer are the same size, so you can choose where these gauges are located. The same method can be applied for fitting the smaller instruments. Either follow your manufacturer’s specs or lay it out as you prefer. The instruments are pretty thin. Each instrument has a bezel screwed in on the backside of the dashboard, which firmly holds in place. The foam-backed vinyl covering the aluminum dashboard also offers a snug fit. After these gauges are secured with the provided screw-in bezels, they aren’t going anywhere.
Step 6: Install Dash in Cockpit
To mount the dashboard into the front of the cockpit, drill five evenly spaced holes into the frame hoop that holds the top of the dash in place. Use an electric drill and a 1/8-inch drill bit. FFR supplies black-finish Phillips-head screws to fasten the dash to the frame hoop.
Step 7: Install Aluminum Brackets at Base of Dash
Two aluminum brackets are used to support the bottom edge of the dash with the 2- x 2-inch frame brace. Use 3/16-inch rivets to hold the bracket to the frame and two of the same screws that were used to hold the top of the dash to the frame hoop. Because the steering shaft provides some support for the driver’s side, we spaced the brackets in the middle and on the passenger’s side.
Step 8: Install Dash
Drill holes in the dash for the three round indicator lights, the low- or high-beam headlight switch, the turn indicator switch, and the black horn button. It helps in drilling these 1/2-inch holes through the padded vinyl if you put a piece of masking tape over the area where the hole needs to be drilled. This prevents the vinyl from fraying too much. Make sure that the dashboard is securely fastened to the frame at the top and at the bottom with the two aluminum brackets, which you just fitted. Place the switches where they look best to you, keeping in mind that they need to be accessible without interfering with the steering wheel, and they need to be within easy reach. Don’t worry if the top curved part of the dash is a little jagged. The entire top edge of the dashboard will be covered by the rolled edge of the body. You will probably be able to see some of the Phillips-head screws, so it’s important to have these screws on an aligned arc and equidistant from each other.
Step 9: Connect Battery Ground
After converting the battery’s negative cable to a side connection, attach the ground to the battery. Don’t connect the positive terminal. You don’t want to get a shocking surprise; your Cobra’s electrical system doesn’t want that either.
Step 10: Extend and Wrap Speedometer Kit Wires
If you install the longer and wider Tremec T56 Magnum 6-speed manual transmission, you need to extend the speedometer kit wires. Solder on some extensions, shrink-wrap the insulation, and wrap the extended speedometer kit wires with electrical tape before plugging the wires into the transmission.
Step 11: Install Gauge Dimmers and Remove Redundant Wires
With the speedometer wires set, hook up the gauge dimmers to the headlight switch behind the dashboard. Some of the wires are redundant in the dash harness because of those provided with the gauges, so you need to determine which ones are extraneous and remove them from the dash harness. We used the wiring harness with the gauges because they are calibrated for these specific instruments. Many amateur car builders might not know to use the wires supplied with the gauges as opposed to the wires in the dash harness, or which wires are redundant in the dash harness.
Step 12: Wire Fuel Gauge to Dash Harness
Wire the fuel gauge to the dash harness, before tidying up the EFI harness.
Step 13: Wire Conduit on EFI Harness
To consolidate and protect the electronic fuel injection harness, install an electrical conduit on the EFI harness.
Step 14: Tape Installed Wires Together
Use electrical tape to separate the wires that have already been wired together from the wires that still need to be connected.
Step 15: Install Coolant Temperature Sensor
Install the coolant temperature sensor in the intake manifold, which is located right next to the coolant inlet/thermostat housing. The Weiand intake manifold has a threaded hole just behind where the coolant inlet/thermostat housing is located that accommodates the coolant temperature sensor. Before installing the sensor with its adapter, apply Teflon putty to the adapter threads.
Step 16: Install Fan Switch
After connecting the fan switch wire at the fan, wire and install the fan toggle switch in the dash. This is a manual switch. You can install a thermostat that automatically turns on the fan, which needs to be retrofitted. The fan comes on automatically via the thermostat in the aluminum radiator. The fan can also be manually activated if, say, you’re sitting in traffic.
Step 17: Inspect MSD 6AL Ignition Box
A good place to install the MSD 6AL ignition box is on top of the passenger-side footbox. We used the rubber vibration-absorbing grommets and some stainless-steel fasteners to install the box, along with lock washers, Loctite, and stainless nuts.
Written by D. Brian Smith and Posted with Permission of CarTechBooks