Here is how I did it. (Long, detailed) (archive)

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Second, you will note that there is a big red wire bolted to the positive battery clamp. This is the feed wire for the car's electrical system. Unwrap the black plastic tape-like wrapping from the wiring harness where it runs along the driver's side inner fenderwell, exposing the red wire back to about where the starter solenoid is. Order some replacement wrapping from Eastwood and use it to carefully rewrap the harness, leaving the big red wire exposed back to the starter. Route the red wire so you can connect it to the big bolt terminal on the starter where the positive battery cable attaches. Cut it to proper length (make sure it doesn't rub or chafe against anything). Crimp a big ring terminal to the end, and seal the connection with some heat shrink tubing. Some ring terminals come with heat shrink attached to them.

Third, remove the old positive cable from the starter and discard it. Buy some 2 gauge welding cable from a welding shop in a length that will reach from the trunk to the starter, through the interior of the car. Have the welding shop attach a ring terminal to one end of the cable. This is the end that will connect to the starter. Allow a few extra feet; it's better to have too much than not enough. Run the cable from the trunk (best place for the battery is all the way forward against the front wall of the trunk, and centered) through the passenger compartment on the driver's side at the outer edge of the floor. Run it along with the other wires that are there; the carpet will hide it. Make sure it's away from sharp edges, etc. Run the cable up under the dash, over the steering column. Buy a rubber grommet (Auto Zone has 'em) that fits over the cable. Drill a hole in the firewall for the cable to pass through so it ends up close to the starter solenoid. Install the grommet in the hole and pass the cable through it. Connect the ring terminal to the big bolt terminal on the starter solenoid, along with the big red feed wire. Make sure all new wiring is away from edges, etc. that could cut the insulation.

Fourth, anchor your battery in the trunk. I used a boat bettery box, but there are other methods. Just make sure it's anchored down tight. Cut the pos. cable to proper length and attach a terminal clamp to the end. Buy a negative cable, with a clamp on one end and a ring terminal on the other end, long enough to reach from the negative side of the battery to some solid metal part of the trunk. Drill a hole through the trunk and bolt the cable end tightly down, making sure there is bare metal where it will make contact with the body. You can interpose a shutoff switch in the negative cable if you wish. (I did, for anti theft purposes)

Now go back to the engine compartment. Note where the old negative battery cable is connected to the engine. It should be bolted to the starter bracket, but some cars may have been changed by now. Remove the old negative cable and toss it. Get a negative cable with ring terminals on both ends at your local auto parts store. Bolt one end to the place on the engine from which you removed the old negative cable; bolt the other end to some solid place on the car frame or body. Make sure there is bare metal where the cable end will make contact with the body or frame.

Back in the trunk, connect both cables to the battery and you're done.
Good Luck
Colin

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