Easy to do Paul, to check the resistance first, in the case of a wire, a few strands left hanging on, in say a pinched wire, won't carry the same current as a complete wire. Say your testing a harness and getting 3 ohms here and 4 ohms there and on the next one you get 12 ohms, there a good chance the problem is in that last section. To confirm it, switch the meter to volts and check to see that there is battery voltage there, then connect a load into the circuit, say a light bulb. If the problem is there, the voltage will fall. You see, the high resistance is always there, but under a load the voltage will drop and the current will rise to overcome the resistance. The problem with test lights is your eyes won't see the difference between 24 and 18 volts, but the starter relay or solenoid will.
And if you test a circuit from the power source end, it will save you testing the whole circuit only to find you had a faulty key switch.
I was always taught that when diagnosing a problem, test the easiest/most likely component first, but everyone has their own way of doing things.
