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Improving your chassis ground (Big 3)

The stock focus battery grounds, engine grounds, and alternator cable are sufficient for a stock car, but when you start putting more draw on the system, its weaknesses show. Upgrading your chassis ground will help your car's electrical system perform it's best. Pretty much anything in your Focus that relies on electricity can benefit from it. That includes the car's own PCM and any ICE/Audio equipment you might have installed.

This was originally posted on Focaljet by Demonfire. For a while, he was selling "BIG 3" wiring kits. You may check there if you are not familiar with crimping thick wires such as these.

Time Required:
1-2 Hours

Tools Needed:

  • Approx 2 feet of 4awg ground cable (black if desired)
  • Approx 4.5 feet of 4awg positive cable (red if desired)
  • 6 ring terminals or lugs of appropriate size for wire chosen
  • 1/2" black heat shrink tubing or other insulation
  • Wire crimpers large enough to tackle 4awg cable
  • Soldering iron / solder / sponge
  • Wire cutters of size large enough to cut 4awg cable
  • Razorblade or other tool to strip cables
  • Heat gun
  • Basic tools to remove bolts: 8mm 10mm & vice grips
  • 6" black cable ties


    The use of high strand 4awg cable is recommended, as it crimps easily compared to other wire, and is much more flexible.

    Cutting the wire:
    Cutting the wire to the proper length is important. If the wire is too short, it will not reach where it needs to go, or it may reach, but be placed under too much stress. If the wire is too long, it may touch something it's not supposed to and it will look unsightly. These are the recommended lengths:

  • Engine to Chassis ground - 8"
  • Battery to chassis ground - 12"
  • Alternator to Battery Positive - 4' 2"


  • Cut wires to appropriate lengths
  • Strip approximately 3/8" insulation off the ends of the cables
  • Make sure your heat shrink tubing slips over the lugs. if it doesn't slip over the ends, cut the tubing now and slip two pieces per wire. if it does, wait until after you crimp / solder.
  • Insert cables into lugs (ring terminals) and crimp. Make sure the wire is crimped enough, but be warned: over crimping can break the strands
  • (Optional, but recommended) Using the soldering iron, heat the top of the lug right over where the opening is where you see the threads. Put a bead of solder on the tip of the iron. when the solder flows to the lug, start feeding solder from the top first (of the wire) to the bottom, filling the "hole" in the lug. let the iron sit on the top of the lug long enough so that you get good contact / flow.
  • Place that wire aside and start working on the next one.
  • When all the ends are soldered, let them cool for a few minutes. Cut heat shrink tubing to approximately 1.5" lengths and slip over the lugs.
  • Heat the tubing to insulate the sides of the lugs that will not be bolted / see ground
  • Disconnect the negative terminal of the battery, and then the positive. If you have capacitors, discharge them.
  • Near the back of the engine towards the passenger side strut tower, locate the rear engine hoist. Attached to this is the engine to chassis ground. Remove the bolt (8mm, I believe) and, keeping the stock cable in place, attach the 8" ground cable to this bolt. Follow the stock ground to the tab on the strut tower, and connect the cable there too. Using cable ties, secure the upgraded ground to the stock one.
  • Remove the small nut on the factory negative terminal. Attach the 12" ground cable to this nut and tighten. Attach the other end of this cable to a nearby bolt. If it is not a factory grounding bolt, make sure the connection is sanded clean to ensure a good ground. If you sand any new connection, spray with electronics grade clear coat or use dielectric grease.
  • Locate the alternator. On the back of the alternator there is a "tower" with a red cap. Remove the red cap.
  • On the back of the tower there is a 10mm bolt holding down the factory alternator cable. **(Note: do not remove this cable after installation)**
  • Try to remove the 10mm bolt. Sometimes the entire tower will twist with the bolt. Using vice grips, grab the tower near the bolt and hold it secure while you loosen the bolt. Attach your alternator cable and the stock cable to this bolt and tighten. Replace the red cap.
  • Give yourself a couple inches of slack before you secure this cable to the firewall or other secure point to allow for engine movement.
  • Run this cable along the firewall to the battery positive, securing it as necessary.
  • Attach this cable to the factory positive terminal, using the small nut on the factory positive terminal, similar to the one you used for ground.
  • Make sure all bolts are tight and all cables are not near any moving or hot parts. If so, cable tie them to a safe place.
  • Reconnect battery. if anything starts to smoke, remove the terminals immediately and check connections.
  • Tighten battery terminals.
  • Admire your work.

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