Can someone explain in laymans terms what i should not test with the load pro ,just so i do not damage anything.I understand how to use the loadpro and what the readings mean ,just not sure about the "ECM Saftey".
I will take a shot at answering your question, knowing that others will surely step in if I get it wrong.
Suppose you're testing a circuit that looks like this: there's a connector with a red wire from the positive terminal of the battery and a white wire to the ECM. The connector is plugged into a solenoid. Inside the ECM is a transistor that the white wire connects to, and that transistor is connected to ground. When everything works like it's supposed to, the ECM transistor switches on and current flows from the battery, through the solenoid, through the transistor inside the ECM, to ground.
Assume there are no faults in this circuit, but you're doing an experiment. You disconnect the solenoid, command the transistor in the ECM to turn on with your scan tool, put your red Loadpro lead on the red wire's connector terminal, and your black lead on the white wire's terminal. What you've done is equivalent to this imaginary setup: a wire with a manual switch in series with a 25-ohm resistor across the two connector terminals, with the switch open, and the non-Loadpro leads of a voltmeter across the connector terminals. With the switch open, no current flows through the resistor. A tiny current flows through through voltmeter with its 10 Mohm resistance, and it will measure 12.6 V or whatever the battery voltage is.
You press the button on your Loadpro, which is equivalent to closing the switch in the imaginary setup I just described. Now current flows through the resistor. The current will be the battery voltage divided by the sum of the resistances in the wiring, the resistor itself, and the ECM transistor. Let's say that current is 0.5 amps.
If the ECM transistor was designed for a current flow that's much less than 0.5 amps, and you press the Loadpro button long enough, the transistor may overheat and fail. The same thing can happen if you use a test light to complete a circuit involving the ECM, and the test light's bulb has a resistance much lower than the circuit's normal load.
I don't know how likely this is to happen because I don't know anything about the hardware inside an ECM. Another way to damage an ECM is to accidentally short the circuit while backprobing both wires in a connector, with the ECM transistor turned on.
To be absolutely safe, you would never press your Loadpro button with the leads inserted into a connector that has a wire running to the ECM.