Originally Posted by Guard Dad

Jueleous,

On many simple systems one of the speaker leads is a grounded (-) lead and one is a hot (+) lead so identifying the positive lead is as simple as using a multi meter to check voltage from each lead to ground, the one with voltage relative to ground is the positive. However since many (most?) newer factory speaker systems are customarily wired "above ground" the standard test can yield similar voltage on both leads. Note that aftermarket systems label all the inputs and outputs as + or - to allow the installer to properly install their components. The car manufacturer often doesn't label these connections because they design the OEM connectors such that they can't be installed incorrectly.