Painless seems to think all power passes through the ammeter rather than the shunt.
They also show the Y/W sense (A on the regulator) attaching AFTER the Megafuse.
If that fuse blows the alternator is going to have a meltdown and possibly catch on fire.
Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.