I have a 2001 Cobra which I only drive when the weather is nice. I got in it the other day and the battery was dead which puzzled me because it hadn't set very long without being driven and nothing was left on that would drain the battery. Anyway, I took the battery out, charged it, put it back in and it started right up. I drove it three days latter and no problems. Then we had two weeks of almost continuous rain and I didn't drive it. The first pretty day, I was going to drive it and the battery was dead again. This time I noticed that the THEFT light in the dash was blinking rapidly. I charged the battery again and the engine started up but the THEFT light keeps on blinking rapidly and I think that over several days this is what drained the battery. I've learned that that light is associated with the securiLock anti-theft system (I know almost nothing about cars) which can go bad. Any suggestions other than taking it to the dealer and paying big bucks for diagnostics etc?

 

First, I'd replace the battery. If its been drained to dead twice, chances are it is going to have a bad cell in it. Automotive batteries tend to not like being treated that way. The second thing I would do is try to find someone in your area with a clamp DC amp meter. This clamps around your battery cable and will tell you how much current draw is being pulled by the electrical system of your car. I don't know what the computer and other accessories pull, but someone at the dealership should be able to look that up for you. If you are pulling more current than what should be normal while sitting parked, you would then have to start pulling fuses to determine what might be the culprit. As far as the security light, it could be associated with the battery going dead twice. Have you checked your owners manual on that feature? Do you have any aftermarket stereo equipment like amps or anything that might not be turning off when the key is off? Power seat button stuck or any other accessories that might not be turning off?
Sounds like possibly two problems but I would start with replacing the battery and testing with the amp probe for current draw higher than normal. Then I'd try to figure out the security issue.
By the way, the THEFT light has to do with the Passive Anti-Theft which is not supposed to let the car start without the key that is coded to your car. The key has some sort of RFID chip inside that must be near the PATS receiver wire near the ignition switch. Had one on my '99 Crown Vic and there is one on my '99 Expedition and also on the '07 Mustang.

Hope this helps you.

 

The battery was only a year old so I took it back to where I bought it to get it replaced under warranty. They tested it and said it was fine. Will check out your other suggestions. Thanks