Re: volvo penta md2010 won't start
Yes, a voltmeter is the right way to approach this. Measure the resistance from the battery negative to the engine ground, there shouldn't be any. Once that is good, switch to voltage and put the black lead on ground and progressively move the red lead from the back of the switch to the starter solenoid checking each connection for good voltage (you need to be pressing the start button). You should find a place where there is suddenly little or no voltage. If there is voltage across your starter solenoid and the starter is not spinner, you likely either have a problem with the solenoid or the starter contact.