the "voltage reducer" gets a 12v hit, then the internals cut it out at a predetermined resistance "heat" factor, be it points opening [like the originals did [i think], or using transistors and diodes like the new "solid state" replacements use to make the "average" voltage seen by the gages around 5 volts. using 3, 1.5v flash light batteries together would give you a good idea how the gage worked, as that would total 4.5v. i have done this in the past, but i limited the connection to short durations only to make sure i didn't hurt the gage being tested. this is why you will see the connection to the gage "flash" using a test light and an original, good working vr. the vr is opening and closing internally, creating a 5v "average" power signal.