2003 Chevrolet Malibu Everthing Off Installing Test Light On Negative Battery

I assume you mean you removed the cable and inserted the test light to look for a drain. That procedure won't work because some computers need up to 20 minutes to go to sleep mode, and all of them draw some current for their memory circuits. You need to insert a digital amp meter and bypass that with a jumper wire each time you change ranges to prevent waking the computers up each time.