whatever you do
DO NOT MEASSURE RESISTANCE ON A OPERATING CIRCUIT.
the only thing you can measure on operating circuit is voltage
Resistance measuring - works by sending a small voltage and measuring the amperage inside the voltmeter.
Voltage measuring - works by measuring the amperage the voltage on the measuring tips causes inside the voltmeter
Amperage measuring - sets internal resistance to next to and needs to be done in line with the circuit you want to meassure.
now, nr 1 is bad because you run extra voltage onto a circuit already at operating voltage, or you reverse the poles etc. you stand a good chance of frying fragile components. nr 3 across two pins of a circuit is just going to be a short really.
measure the voltage against the body (ground) and then go pin to pin and see if there is any signals i.e. 5v, 12v etc. i would guess the frequency of the signal is going to be too high to pick up with a voltmeter to see the signal pattern, so you are most likely looking for a steady voltage reading, if it bounces around you got nothing.