My 2005 won't turn off and has even started on it's own with no key in ignition...just statred happening last night. Had t disconnect battery to stop car. Seems like car doesn't realize the key is out!

Question moved to model category.

When you disconnect connectors under the dash, you are likely to cause issues with the anti theft system, when you disconnect the battery, you DEFINITELY do. Now you need to reset the security system. Is the anti theft light on solid?

https://www.google.com/search?q=2005+infiniti+g35+reset+security+system



Or you get an auto electrician to diagnose with a professional grade scan tool computer.

https://www.google.com/search?q=auto+electrician+near+me

..

need to reprogram ignition key security system when battery disconnected. turn ignition key to the on position for 3 to 10 seconds until the lock light goes out then start vechicle.if lock light dont turn off turn ignition switch to on position 30 seconds until lock light turn off.

The alarm system somehow got activated , this is usually because the battery becomes discharged or disconnected try doing this:
Remove the key from the ignition
disconnect the negative battery terminal
put the key back in and turn to ON
exit the truck and leave door open
reconnect the battery terminal
get in and leave door open, if the alarm horn stays off it should start.

try jumping if it jumps or you get power from a jump its your battery it can die over night this is common runs good one day then will not do it the next i would start there first if it turns over after a jump that is your problem.Replace the battery most batteries only last up to 18months

Hi I had this happen last night but both of my headlights were out (one had been for a week but the other also went last night) I assumed it was to tell me there was a fault as it's stopped now I have replaced the headlight bulbs

You may want to try to slightly push / pull your vehicle to take weight / tension off the transmission, which in turn will allow you to turn the steering wheel enough to see if the ignition switch can be turned.

I hope that you have disconnected the battery fire could happen relay click's but will stick at drain could be the fuel pump you hear with the continuse click you might have a shorted starter.I think thats the first place to start.A bad ignition switch will cause this to happen sometimes?

under what condition the car won't start?
is it when the car set over night, a few hours or after a few minutes.
does it make any noise or click when you try to start?
does the engine even turn over at all or just silent?
if nothing happen then may be the starter, switch or fuse.
if the engine turn but won't run then may be the ignition system or fuel system.

Poor connections at the battery cables to the battery

try checking the main relay under the dash