Generator?

Start the engine and take another voltage reading at the battery and see if the voltage is higher than the first reading. If the voltage is higher then he may not have the ammeter installed right or on the right wire. It should be the wire coming from the generator to the ammeter and then to the junction block if it has the one wire generator as for the 9N 2N. It will have the cutout mounted on top of the generator. If it has a voltage regulator and a two brush generator the ammeter could still be installed wrong if the second voltage reading is higher than the first reading.

If there is no higher second voltage reading the generator may not be charging and may only need to be polarized. This is easy on the one wire generator. Just use a short jumper wire to momentarily strike a spark from the wire coming to the cutout over to the wire coming out of the generator. Be sure to have the battery connected with a positive + ground.
With the later generators with the voltage regulator make sure that the wires are all connected at the right places on the generator and the regulator. The wires can be traced from one point to the other by using an OHM meter to check for continuity from one end of the wire to the other with both ends disconnected. Then put that wire on the post is should be on like say Gen to gen and Fld to Fld etc.
Thees generators can also need to be polarized when trouble shooting one that is not showing any charge. Ask Claus how to do this one because I have forgotten how to do it. I would not like to tell you wrong and have you damage the generator or more likely the regulator.