The test light is one of the best tests.You will have some draw as it keeps the computer and radio alive but will be very dim.Most will light the light fairly bright when you first hook it up as it powers up all memories.Just make sure the light has a bulb.Ones like Snapon that uses a fuse type wont work right.Ive found most are interior lights or the alt.Did a lot of electrical work when I was at the shop.Jeeps had some bad wiring.Rocky