Simple way to measure amps with a volt meter?
How you use a voltmeter to measure current is by inserting a current sensing resistor into the circuit, and measuring the voltage across that resistor.  The resistor has some small value that does not disturb the quantity of current (at least, not very much). you have to take care that it has enough power dissipation (\$I^2R\$) for the expected maximum value of \$I\$.  

The scale of the meter will be sensitive to the value of the resistor, so you need to be able to calibrate your instrument. For instance, use a known, accurate current source and mark that off on the dial. You could set up a potentiometer to calibrate it. The nice thing is that the current sensing resistor is a low-impedance voltage source. It can feed some some reasonably valued potentiometer.

There are ways to measure current without breaking circuits. That is done with a current clamp. That's a separate instrument from your volt meter. You could build one yourself, using the volt meter for the instrumentation.