The clock radio stays on with the ignition key turned off

SOURCE: radio/clock would reset every time (almost) when

check memory fuse,fuse panel or back of radio,3 to 5 amps

SOURCE: I have a 99 Camaro Z28. The clock radio stay on

Is the radio an aftermarket radio or an orignal equipment radio?

SOURCE: something is draining the battery.

Assorierie delay relay might be sticking or a door switch is'nt working ( driver's) The assories are supposed to stay on even after you turn off the key and remove it but when you open the door to get out thier supposed to shut off. The body control module controls this realy but I have found it to be very relilible. Peaple adding aftermarmert radios are almost always at fault as they wire the radio to both key on power and assorie delay power. This hard wire makes the whole system stay on. Let's say that's not the problem. To find a draw ( power loss when shut off) you have to make the car ( think ) that it's shut off or quite a few things will be on. These are controlled by the body module. With the window down and the door open and the dome light fuse pulled open the hood and disconnect the battery. You'll need the code for your radio before you disconnect the battery or the radio won't play till you type in the correct code. You might have this code in your papperwork or the dealer's parts dept can come up with the number if you provide the VIN and show something that says the car is yours ( insurance card). With the battery disconnected connect a test light between the battery and the battery cable, The light will come on ( if you have a draw). Batteries will kill themselfs also as they get dead cells and been dead too often. But you said the radio and the power windows still work after removing the key, So the battery might be bad now but it did'nt start this problem. Watching the test light pull fuses one at a time till the light goes out. then reserch this fuse to see what it does and decide if you can do without it or if it's nessary what to do to make it turn off. Brake light switches stick, Alarm systems need reprogramed, realys stick on. As your looking for the draw another way to look is to open the hood and take the cover off the fuse relay panel and touch the relays one thats warm is on, If it's on it's sending power to somewhere unplug it and see what doesn't work... It may be stuck on or something is comanding it on. If it's commanded on, a scanner needs to be connected to the system and the body functions looked at and the fault codes decided opon and the correction followed. ECMs and BCM's don't fail very often as their expensive too, so you might want a professional to help you before you go buyng expensive parts that your not likly to be allowed to return.