Battery Placement

Discussion in 'Fox 5.0 Mustang Tech' started by sen2two, Jul 27, 2013.

  1. i am moving the battery to the back of my car. i am wondering where is the best placement? my guess is on the passenger side just slightly behind the rear axle.
  2. As far back and to the right in the hatch/trunk as you can practically mount it.
  3. Driver side or center. The reason I say that because if you look at pics/video of any Fox pulling the front wheels off the ground, the driver side becomes the torqued light side.

    If doing road courses, I would likely mount in the center.
  4. i am planning to stitch weld the chassis very soon, so that should take care of most of the flex. subframe connectors will come later down the road. but the back right seems to make more sense than center to offset driver weight...
  5. You should save the nickles and dimes you're going to spend on relocating the battery and get those sub-frame connectors in first followed by torque box reinforcements.
  6. you dont think stitch welding will be good enough for the time being. it adds an incredible mount of stiffness and rigitity to the entire chassis.

    also, this is daily driven car with a goal of only mid 12's.
  7. I do not. The most flexible portion of our chassis are the sections between the subframes. Even driving around town with stock power causes it to flex. Most Fox bodies (20+ years old) will show signs of that flex in the paint on the A-pillars.

    Jack up any corner of your car and you can measure the amount of flex from front to back. Do the same on a car that has had full length subframe connectors installed. The difference is pretty dramatic.
  8. I second you need sub frames, they make quite a difference. You put the battery on the right side because that is the first tire to spin - a lot of people used to install air bags in the right spring for thee same reason. It also offsets the driver's weight as you mentioned. Moving the battery to the trunk moves the center of gravity rearward, improving handling and traction. Need to minimize how much weight you add with cabling from the trunk to the engine in the front....
  9. I put a xs s925 battery in my spare tire well. It's hidden and starts my car with no issues what so ever.
  10. Rear mounted battery ground wiring. Follow this plan and you will have zero
    ground problems.

    One 1 gauge or 1/0 gauge wire from battery negative post to a clean shiny spot
    on the chassis near the battery. Use a 5/16” bolt and bolt it down to make the
    rear ground. Use a 1 gauge or 1/0 gauge wire from the rear ground bolt to a clean
    shiny spot on the block.

    One 4 gauge wire from the block where you connected the battery ground wire to
    the chassis ground where the battery was mounted up front. Use a 5/16” bolt
    and bolt down the 4 gauge engine to chassis ground, make sure that it the metal
    around the bolt is clean & shiny. This is the alternator power ground.


    The computer has a dedicated power ground wire with a cylindrical quick connect
    (about 2 ½”long by 1” diameter. It comes out of the wiring harness near the
    ignition coil & starter solenoid (or relay). Be sure to bolt it to the chassis ground
    in the same place as you bolted the alternator power ground. This is an
    absolute don’t overlook it item for EFI cars

    Note: The quick disconnect may have fallen victim to damage or removal by
    a previous owner. However, it is still of utmost importance that the black/green
    wires have a high quality ground..

    Picture courtesy timewarped1972 [​IMG]

    Crimp or even better, solder the lugs on the all the wire. The local auto stereo
    shop will have them if the auto parts store doesn't. Use some heat shrink tubing
    to cover the lugs and make things look nice.

    For a battery cut off switch, see
    is the switch is the installation instructions.
    Use the super duty switch and the following tech note to wire it and you will
    be good to go.

    Use the Moroso plan for the alternator wiring and you risk a fire. The 10 gauge wire they recommend is even less adequate that the stock Mustang wiring.

    There is a solution, but it will require about 40' of 18 gauge green wire.

    Wire the battery to the two 1/2" posts as shown in the diagram.

    The alternator requires a different approach. On the small alternator plug there is a green wire. It is the sense lead that turns the regulator on when the ignition switch is in the run position. Cut the green wire and solder the 40' of green wire between the two pieces. Use some heat shrink to cover the splices. See for some excellent help on soldering & using heat shrink tubing.

    Run the green wire back to the Moroso switch and cut off the excess wire. Try to run the green wire inside the car and protect it from getting cut or chaffed. Crimp a 18 gauge ring terminal (red is 18 gauge color code for the crimp on terminals) on each wire. Bolt one ring terminal to each of the 3/16" studs. Do not add the jumper between the 1/2" stud and the 3/16" stud as shown it the
    Moroso diagram.

    How it works:
    The green wire is the ignition on sense feed to the regulator. It supplies a turn on signal to the regulator when the ignition switch is in the Run position. Turn the Moroso switch to off, and the sense voltage goes away, the voltage regulator shuts off and the alternator quits making power.

    The fuse & wiring in the following diagram are for a 3G alternator. The stock alternator uses a dark green fuse link wire that connects to 2 black/orange wires. Always leave them connected to the starter solenoid even if you have a 3G alternator.


    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Everyone should bookmark this site.

    Ignition switch wiring

    Fuel, alternator, A/C and ignition wiring

    Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs

    Vacuum diagram 89-93 Mustangs