Determine vehicle electric load and amps used

[mrexp21]

Using which device or method, I could calculate and determine total electrical loads and amps used in a vehicle ?

 

[Tmoose]

Depending on the accuracy you need, something like this?

http://www.sears.com/shc/s/p_10153_12605_03482369000P

With all lights and accessories on, and the engine off, a clamp around a battery cable would indicate everything except the ignition etc and ECU.

Running, the big alterrnator wire might tell the tale.