starting trouble still

First test. Take the car down to autozone and have them test the alternator/battery. I know you replaced them, but you never know if the "new parts" are really new. Even from autozone. I have friends that work at autozone and they have some strange stories to tell!

If the battery/Alt test fine, here is step #2:

Have someone hook up jumper cables to your car and see what happens. If it starts fine, you have bad cables. You need to look at your cabling. Clean every single contact (battery connections, motor ground, starter contacts, secondary ground if there is one). If that doesn't work, replace the main ground cable. Then replace the main positive wire if that doesn't work.

Give me some more information on the car. Can you do a clutch start and the car will run fine (assuming you have a standard)? Can you turn all the lights on, press the brake pedal, and the voltmeter doesn't drain much?

If you are only having starting problems, then I assume it is one of the cables connecting to the starter. You replaced the main hot wire to the starter, so you need to check/replace the ground and ignition wire. Hook up a voltmeter to the positive and negaitve terminals of the starter. You should ALWAYS see 12V. Now hook up the voltmeter to the ignition wire and ground wire. You should see 12V only when someone turns the key to start the car.

If you don't see 12v on the accessory wire and ground, you need to look into the accesory wire. Since you see 12V with the positive and negaitive wires, they must both work. So now all that is left is your ignition wire.

My dad's maxima would not start. His starter/batt/alternator were fine. All cables were clean, no problems. But his ignition switch went haywire, so it wasn't sending the 12V to the starter and letting it start.

Check the connections to your ignition wire. See if you have continuity along the wire. If the wire has continuity, then I would check the ignition switch (connects to the back of the key cylinder). When you turn the key, a plastic tab turns the ignition switch to the proper spot. Run a wire from the positive terminal of the battery to the starter wire on the ignition. If the starter cranks, the ignition switch is bad. 20 bucks, and you are ready to go!
Scott