Re: Neg side of battery and ground same thing?
Well, all grounds lead to the neg battery post. The difference sometimes can be the quality of the connection/ground since poor grounds affect performance. You can use a multi-meter to test continuity and measure the resistance... The less resistance, obviously, the better ... I would be surprised if you just cannot find a good, clean ground point and go with that... Monitor that the wires are not getting overly hot when running the fan...that would be a sign of high resistance