When using a voltmeter, if the positive lead is at a place with a higher voltage then the negative lead, will the voltage be registered as negative or positive?

 

Positive; by convention, (unless someone has reversed the leads) the red lead is usually positive and the black lead is negative.

 

There are such things as high negative voltages. A digital meter should display the polarity. The meter will also have markings for lead placement indicating which is the positive lead and which is the negative. If using an analog meter, it will only give an upscale reading if the positive voltage is applied to the positive input.