Doing
an EFI swap on an early model Mustang doesn't absolutely require
relocating the battery, but it does make it easier and cleans up the
engine compartment. There are 4 basic options when it comes to the
battery:
- Do nothing, this
leaves you with a cramped area to install your breather, and makes for
lots of exposed wiring under the hood.
- Turn the
battery box sideways (using a 69-70 battery tray), this works better for
the air filter but
still limits the space and the wiring is still there
- Relocated to the battery to driver's side front
apron; this fits the original wiring scheme of the Fox EEC-IV
harness. It still leaves all the wiring exposed, and you have to
fabricate a new battery box and support structure, as well as relocate
the overflow tank.
- Relocate
the battery to the trunk. This is the most visually appealing
and provides the most room for the air filter. The drawbacks are
that you have to run extended cables and deal with a battery in the
passenger compartment.
As
for the latter, there are two choices. You can purchase a sealed
battery, such as an Optima, and mount in the truck using standard mounting
hardware, or you can use a standard battery with a sealed battery box
vented to the outside. For this installation, I chose the
latter.
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Trunk
Mounting: In
order to mount the battery box on a level surface, The entire trunk was
leveled using a 3/8" plywood. (Photo 1) Underneath the plywood,
1"x1" steel angle was used in 3 rows to brace over the fuel
tank. (Photo 1) The plywood is cut in two pieces and spans the entire
truck, including dropoff areas. This allowed the relocation of the
spare to the drivers side. The spare tire hold-down hook runs
through the plywood and through a hole in the angle iron. The tire
is secured to the hold-down. (Photo 4)
The
battery box is secured to the using 1"x1" angle iron as
footings. (Photo 5) These are bolted through the plywood,
through holes in the angle iron and secured using clipnuts. To
remove the battery box, the bolts are removed and the box slid forward.
Inside the box, steel straps are mounted up the interior sides of the box and attach to angle brackets
which secure the battery inside the box. (Photo 2)
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Cable
Routing: Three
wires are routed from the aft battery box (Positive, Negative, and direct
power to the vehicle). The following series of photographs show the
path for the positive cable.
The
positive cable runs from the battery box, under the rear seat (Photo 2),
through the passenger door well, and into the panel behind the
kickboard. From here, a hole is drilled and the cable routed behind
the fender up to the splash panel (Photo 3). The cable then runs along
the top of the fender apron till it reaches the old battery tray area.
(Photo 4), Here, the cable is routed into the engine bay and down to
the starter solenoid, which has been relocated down to just above the
framerail. (Photo 6). At final installation, this cable run is covered
with a large rubber hose that is cut and slides over all wiring protecting
it from damage. Rubber grommets secured with silicone adhesive are
used in all areas where the cable passes through a panel. Rubber lined
adel clamps are used to secure the cable along the run. In any
locations where chaffing could occur, insulation is installed (Photo 2). The
ends are swaged and soldered to the end of the cable.
The
negative cable runs out of the battery box, and down through a rubber
grommet in the trunk floor. The end of the cable is soldered and
swaged, and secured to the rear frame rail. A clean surface and strong
bond is needed to ensure a good vehicle ground.
The
third wire is optional. I chose to run an independent 8 gage wire from
the positive post of the battery along the drivers side and up behind the
dash in order to feed the vehicle's main power distribution system.
This replaced the original Black/Yellow wire that drew vehicle power
from the + post of the starter solenoid. The reason this wire
was added was to shorten the total wire length to the main fuse panel, and
to avoid any spikes or voltage drops from picking up the power at the
solenoid.
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