Sluggish starter voltage drop test :
Note, when doing voltage drop test, the voltmeter probes should touch the battery post, and solenoid post, not the cable or terminals on the cables.
Positive probe to positive battery post.
Negative probe to negative battery post.
Crank starter, note the voltage reading while starter is cranking.
This is your system cranking voltage, it should not be lower than 9.5v
Next:
Touch positive probe to the positive post on the starter solenoid, touch the negative post to the body of the starter.
Crank starter, read the voltage while cranking.
The reading should be the same (within .5v) as the system cranking voltage.
If the voltage readings are the same (within .5v), it means the starter is getting full system cranking voltage, so if the starter is sluggish, the problem is somewhere in the starter, or there is a mechanical issue that the starter cannot overcome.
If the reading is low, it means the starter is not getting full system cranking voltage, don`t condemn the starter yet…there is most likely a problem in either the positive battery cable circuit, or the negative ground circuit.