Never noticed this before. Don't know why it can't be wired to ammeter as the note says.
Click
This may be a good option for you.
Otherwise, Classic Trucks is where you can get original type parts. They have the VR.

Rockauto (kevinski) has a much BETTER Warranty and price. Theirs is a Wells unit, not Chinese. Well known name. Mfg'ed. USA and Mexico.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn