I've got a vampire drain on my battery!

I've had to jump my 2000 Ford Contour SE, 138K miles, 3 mornings this past week. It's getting worse. Before it was about once a month. I bought a new battery at Auto-zone. 590 crank/amps.

They check it every time and tell me the battery is fine and it is charging correctly. Must be a short somewhere.

What I've noticed:

If I parked my Contour the night before with radio on position, fan blower (switch) on position, battery seems to drain overnight and will not start the next morning. Of course everything is off. I even wait to see if interior lights go out when door closed and locked.

If I park my Contour with everything Switch OFF, it will start the next morning however not with a very quick start-up (like a new battery) but it cranks and starts after a second or so.

I was thinking the Contour MAY have a SELENOID that kicks in with the keys in the "ON" position. Keys "ON" position causes panel idiot lights to work and blower fan will come on if the fan switch is in "ON" position, wiper blades motor will work.

"Accessories" key position just lets radio work. Should I be able to see a slight drop in
voltage across battery posts if every thing is off however I switch the blower fan switch inside car?

I'm thinking a component is causing a vampire drain on the battery even though key is off. This is why I switch everything off. I'm going to unhook the open door light that come on under the dashboard to see if this is causing the vampire drain on the battery.

I've already put $5K into the vehicle. KBB says its worth about $2K. All original parts, nothing fancy added. Completely stock and has always been garaged. Paint very good as well as interior.

My wife wants me to keep it and give it to my son, however it has this electrical problem. I'm not a mechanic and I don't have mechanic's tools yet I have a volt meter and I know a little about electricity. I can't keep throwing money at it to get it fixed!

Any suggestions?