Grabbed this off the web site. It made it very easy to understand:
Originally Posted by av8r
Correct in principle. However take a look at the specs on this unit. It only uses 3 wires and one end of the shunt has to be grounded. Placing it in the positive side of the alternator and connecting the wires as directed may cause a dead short to ground with associated smoke and melting wires.
I wired mine in between the batterie negative to the chassis ground And wired all of my electronics to chassis ground
By Stephen meagher on August 31, 2015:
The black and yellow wire connect across the shunt with the black lead on the most negative side. The red wire must be connected to a positive voltage between 5 and 30volt all 3 wires are only voltage sense and carry NO current.
The wires are very flimsy so strip with care.