I with W.M. on this. We need to know what your working on? Is it EFI or not. If it is, you will have a small drain due to the ECU has to keep it's memory so you will have a draw but not enough to light a test light. Usually the ECU draws .5 amps or less which isn't enough to cause your battery to drain that fast unless you have a bad cell in your battery. Take your battery to your local parts store & have them load test it. Also, make sure the top of your battery is clean & dry with no corrosion. I have seen batteries drain due to the corrosion/acid build up on top of the battery. It will actually short across the top from positive to the negitive & cause the battery to drain. You can use a baking soda mixed with water & an old tooth brush to clean the connections
