First read my Cave, Alternator Sense
including link at bottom.
My guess is their messing w/ sense wire. 0.
6v means they likely just adding a diode.
Problem is fooling w/ sense wire often hides other problems, like Most issues this "fixes" can be iffy ground(s).
example, Brighter HL... See my Cave, Headlights
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)