If you are using a digital voltmeter, they have a very high input impedance, on the order of 10Mohms. If your battery measures 12V and using your battery to ground is 11 Volts, then you have about 1.1mA of leakage. This is normal for automotive alternators.
If you have an old analog meter, try again using it. It has a lower impedence and will read a much lower voltage; <0.1volt if everything else is correct.
Or try placing a temporary 12V lamp between the Batt(-) and ground. An instrument light bulb or a brake light bulb will suffice. If the bulb will not light, then measure again using the digital meter. I'd bet that the voltage with the bulb in place drops to zero. If the bulb lights, then you most definitely have an issue.
My bet is that there is nothing wrong with your wiring (yet
)
_________________
Chuck.
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