voltage drop test is done with a digital multimeter only. Its not too hard, just need an understanding of how electricity works.
to do a simple VD test, take a multimeter, select DC volts, touch one probe to the battery positive and one to the starter positive lug (battery cable lug).
crank the engine, if you see about 1 volt there, there is a massive voltage drop in the circuit, repair and retest.
same can be done for other circuits like ground circuits.