load testing

hello, I'm wandering if there is a rule of thumb on load testing? Like as far as what should I be load testing before I make the call that a ECM is bad or a MAF sensor is bad or like a coil plug is bad, or even a crank sensor? What should I be load testing and what is a rule of thumb on the amps of load depending on the circuit? Thanks 

Load Testing refers to testing the ability of a circuit/wire (or power source), to support enough current flow to adequately energize a component. You cannot "Load Test" a MAF senor but, you CAN Load Test the wires that energize the MAF sensor. 

A load test is, simply, checking for a voltage drop between the power source and the component/load that is being energized. 
The rule of thumb for Load Testing is to use a component/load that draws the same amount of current that the circuit is designed to carry. The best component/load to use for a load test is the actual component/load, i.e sensor, bulb, motor, solenoid, etc. that the circuit was designed to energize. If there is a question as to whether or not the actual component is good or bad, a substitute load can be used. An ECM, MAF sensor, or Crank Sensor draws very little current, and an incandescent test-light would be a sufficient substitute load. Other components, such as a headlight, fuel pump, or blower motor, draw much more current, and an incandescent test-light may not be a good choice for a substitute load. Some people will use a variety of light bulbs or headlights to substitute loads.

If you know the power source voltage and the resistance of the load, you can use Ohm's law to calculate what the current flow will be.

I=V/R, were "I" is Current, "V" is Voltage, and "R" is Resistance.