yes use a volt meter.
basically you are checking for a voltage difference in the sensing line or the field line.

1 field line goes to the vr the other ties back into the key on power from the ign 1 on the key.

here is how I look for voltage drops.

with the car on run, but not running.
you check with the voltmeter using the battery ground.
check against the pos of the battery, see what the voltage reads.
then check voltage at the sensing line of the VR.
Then check voltage at the field of the alt. with the vr plug pulled, (assuming this is a dual field alt using the later triangle plug vr), one of the fields will be 0, the other should be battery voltage.
you can then trace back to the bulkhead to see if that is causing the issue or a bad connection somewhere else.

you can also transfer the ground to the body of the vr as well when checking the sensing line voltage and to the body of the alt for the field to see if there is a ground issue.

generally speaking I would bet you will see almost 1 volt drop meaning you need to clean up the bulkhead connector or find the bad connection.
if swaping the ground gives you a bigger volt diff, then you have a bad ground somewhere.