Brand new battery and alternator but the battery still goes dead over night.

Check and clean the earth strap to make a good connection.

Is the alternator charging , with engine running connect a volt meter to battery should show around 14.2 volts , is there a short , remove leads from battery over night , if it starts in the morning there is a short circuit, if the battery is nun down it's faulty even though it's new .

put kill where? at battery post, and is just a switch,
not those dynamic battery drop relays?
if the battery goes dead with the neg. lug pulled the battery is bad.
end of life , battery.
the lug pull never lies.... ever.
if stays ok now this is called battery phantom drain.
(or aka. dark currents)

finding cause takes an ammeter. any,
here is all ways to find a drain.

http://www.fixkick.com/drain/drain.html

Hello Jr, The fact that the battery goes dead even with a kill switch would lead me to think the new battery is defective.

Large wire is possible hot wire to altenator. Should have B+ voltage at all times. Need to do an amperage draw test and start eliminating sub systems to determine root cause. Also would like to point out a new battery does not mean defective free. would load test to ensure no dead cells first.

Well, something is on if the battery is dead. Pull the interior light fuse, and the clock fuse, disconnect the negative battery cable and put a 12 volt test light between the battery terminal and the cable...Likely it will light. Then pull fuses one at a time and observe if the light goes out. Keep disconnecting until you get the light to go out. Do not rule out the new alternator, stuff happens.

If it was an alternator related problem the car would die while it was running. it could still be a bad battery. i have gotten a few new batteries that were bad.

try this:
-drive the car for about 15 mins to make sure the battery has a good charge
-after you park it, then disconnect the (-) neg cable from the battery
-let the car sit over night with the battery disconnected
-the next day hook the (-) neg cable back up to the battery and try to start the car

if the battery is good, it will start normally
if its bad you'll get the -no start- problem

If the battery is good, you have a parasitic drain some where in you electrical system.

If the vehicle sit for a period of time, even over night and it won't start with the new battery and alternator, you have a dead short drawing voltage from the battery until it goes dead. Disconnect the positive terminal from the battery and connect a test light to the cable and touch the battery positive post with the other end of the tester. If the tester lights up, you have a draw on the battery causing it to go dead. Now you need to pull 1 fuse at a time while the tester is connected to see when the light goes out. When it dies, that is the circuit that needs to be traced to find the faulty switch, bard wire or whatever is the cause. Good luck.

Most likely the diode from the alternator is leaks draining the battery. If you believe your battery is good then recharge it to full level then do the followings: 1- Disconnect negative cable from the battery over night to see how weak it is in the next morning. If it is bad then it is the battery no other thing. 2- If it is good, take off wires from the alternator for a night, next day battery is still good then there is a problem with the alternator diode. Hope this can help.

have you had the alternator checked out?