This is the old battery in the trunk trick! Not necessary but what the heck! We have all seen the relocation kits and I am going to use a marine battery box because we can still use what little space is left in the trunk. The other piece of this project is the fact that the spare tire sits right where the battery needed to end up. We had to find a new home for the big rubber round thingy before we plant the battery. Really another project but since it has to be done to get the battery in place I included it all here.
We have to move the spare to make room for the battery so we are remounting the spare in the middle of the trunk. The actual mount is a simple fabricated T shaped affair. It bolts to the rear end hump and straddles the gas tank. Some 3/4 square tubing and and a couple of sections of flat stock are all of the components. The main leg incorporates a hand formed loop that will allow me to reuse all of the stock spare mounting hardware. The rearranged trunk moves the spare tire as far back as possible toward the seat back. Simple and effective. But this just makes the leftover space issue obvious.
The marine battery box, base mount, 2 gauge cables and assorted size wire are all readily available pre bundled or separately at many auto parts stores. The starter solenoid is relocated to the rear also. The wiring diagram and the details are in the tech article electrical section.
I am using a group 35/72 dual post battery. The battery box is windowed for access to the side terminals in case we need to jump start. A 2" hole saw made the openings neatly. The battery hold down bolts are anchored in the base assembly and go thru the box so that if we need to remove the battery for some reason you can lift the box and battery as a unit. To hold down the battery I just fabricated a pair of L brackets that attach to the ears normally for the carry handle.
A Ford fender mount starter solenoid is mounted right on the side of the battery box. Because the case is plastic a ground wire will go from the solenoid base to the battery ground terminal. You can use whatever solenoid you want but we chose to use a late model Ford version that mounts flat and hooks up a lot cleaner than the earlier round unit. Rumor has it that it is more durable. A master shutoff switch may be installed but I am not sure where yet.
The battery box is in it's final home. Bolted down directly over the rear frame rail. It took a bit of fidgeting around to find a suitable position and to make it some sort of level because the trunk in that area is actually sloped to the rear. But after a bit of prep it is now securely fastened down and level. One small change was to re index the starter solenoid 90 degrees in order to let the power cables hook up in a nicer configuration. The 4 cables (Primary battery, charge, start and ignition) are run over the wheel well housing and into the open chassis sill channel and are soon to be passed into the engine compartment in the front foot well.
I have chosen to route the primary cable and harness through the passenger compartment and not under the car for a variety of reasons. Initially they would have been along the edge of the floorboard. As another brain-lock fades away (Remember the 54 Ford gas tank sender!?) it dawned on me that, like most cars, Mustangs use the sill channel as the routing area for the front to back wiring. The main harness goes down the drivers side sill which leaves me with the passenger side sill free to run my back to front battery cable and harness. It works out perfectly! Protected and hidden . They go all the way forward to the front foot well and come out in an access hole in the front kick panel. The cool part is this is hidden by the kick panel trim.
Up in the engine compartment - we started the removal and/or relocation of our starter solenoid and charging parts. When we removed the battery and battery box it was discovered that below it, where the reinforcement plate is, was badly rotted. ( Another common problem with these beasts but still a problem. ) The starter solenoid was removed and we have decided to track all the wiring for it back into the passenger rear corner of the engine compartment and do the hookups there. As for the start cable ... After locating a suitable pass through location in the passenger foot well it became apparent that if something were to happen to this cable the whole thing would need to be replaced. The solution we came up with is a Heavy Duty Battery Feed Stud (1). This will allow us to use a separate short cable from the fire wall to the starter. And with the headers it is a real good chance this is going to get toasted!
The pass thru is installed in the front passenger foot well .The main power feed lug is a single 3/8 insulated stud. This will be covered by a battery terminal end cover. The alternator feed, ignition and start wires are going thru a grommeted hole just under the heater box to a 4 lug bar to join the front and rear feeds together at the fire wall. A covered mega fuse holder and an 175 amp mega fuse now reside in the alternator feed line. A ground lug was made on the rear package tray support. Since this is a unibody car it should be more than adequate.
I finally got around to installing the master cutoff switch. We had installed a large bolt as a chassis ground earlier on the hinge mount. I fabed an aluminum panel to hold the switch and then went hunting for an appropriate location to mount it. It ended up being bolted to the same passenger side trunk hinge plate with the ground bolt. High enough to be out of the way but easily reached and close enough for some short cabling. A piece of new cable and the unit was usable.
The trunk is just about done. Mustangs don't have a lot over the gas tank which IS the main trunk floor. So I decided to put in a simple mat over the gas tank to protect it at least a little bit. The mat was padded and layered with PVC sheet and some original speckled trunk mat material. Some small fingers underneath keep it from scooting around. The installed cables going to the front have been clipped in so they don't move around.