The manual says: remove main fuse and connect ammeter across main fuse terminals and voltmeter across battery terminals.
Disconnect the black wire from the reg/rec coupler. Start engine and check charging output at the speeds as follows:
A V
1,200 rpm (+) 8A Above 12V
3,000 rpm (+) 12.5 A 14-15 V
8,000 rpm (+) 13.5 A 14-15 V