How to stop drain on battery with key & all accessories turned off?

With ground cable disconnected from battery & a test light put between the ground cable & negative battery post the test light stays dim & blinks about every 2 seconds consequetively. I have pulled out each individual fuse & no one fuse stopped the test light from blinking. Inside cab by steering column I disconnected several small electrical boxes that are as small as a pack of cigerettes. Disconnecting these made no difference with the test light. One of the small plastic boxes on the fire wall in the cab makes a faint beeping noise a little like a car alarm. Im at a loss as to what to do next.