Might not work with things like a stereo, optional alarm, etc. that will pull current when the key is off. Best thing is to pull all the fuses and then install the test lamp between the battery terminal and the cable end. Then with the key off you can simply install one fuse at a time until the light comes on. If it comes on with the radio fuse, then you can remove it and leave it out until all the others are installed and checked.Okay put a 12 volt lighted tester between the battery ground and the battery
If you have a short the light will stay on when the truck is turned off.
Try pulling fuses one at a time until the light goes out that way you know wher to start.