I dont know if you can test it or not. Also not sure if I have ammeter or voltmeter (i hate electrical lol) on the gauge it says 8 13 18 (i think those are #'s), which gauge is it, and is there any way to test it? I dont know if its my gauge or if its my alternator. MY gauge randomly dips down to near 8 then springs back up to 13 and runs there alonggggg time then will dip down again. Usually only if im runnin a constant speed, like down the interstate.