Steve
You can test for a current draw with a standard 12v test light.
With everything turned off, disconnect either battery post and connect the test light in series with the disconnected cable and the battery post. A small draw will burn the lamp. Then disconnect wires, fuses, ect until the light goes out. You may want to start with the large postive wire on the alt. Using this method is easier than trying to detect a small movement on a gauge. If I can help, I am
ron621@msn.com. Good luck.
RON