[Cubcadet_107]

Here's the 122 diagram:
WD_1x2_3.jpg

Here's the diagram for the next tractor series (which came standard with an ammeter)
WD_1x4_5.jpg

All the wire colors are the same between the two. The green wire runs to the neg. terminal on the ammeter rather than going directly to the solenoid. Then an additional red wire (not original to the 122's harness, you'll have to add that wire) runs from the pos. terminal of the ammeter to the same solenoid terminal where the green wire would have gone.

Hope this helps