If you want to measure DC amps use a section of the power wire and measure the millivoltage drop across it when the system is on.

If you have 4 awg wire using "probes" 3 feet apart with a 1Mohm or better input to a multimeter you should read about 74.55mV @ 20 deg C with 100A draw. I have used this method by sticking pins through the insulation and hooking the meter leads to those. Accuracy depends on the meter you use.
J