Battery gauge not showing any charge. Suggestions welcome

Good evening,
Viewed a Daimler 250 V8 and the battery gauge needle did not move when the engine revs were increased but showed a discharge when the electric cooling fan cut in whilst the engine was ideling.
I guess the alternator is defective but would appreciate any other possibilities.

I would have thought the Daimler would have a generator?

Thanks for your reply.
I assume a NZ generator is the same as a UK dynamo.
The earlier vehicles were fitted with dynamos but in 1967 they were replaced with alternators.

Correct, but you mentioned that you were seeing a negative figure on the age which lead me to think you were looking at an amp meter rather than a voltage gauge.
From memory the change to an alternator would coincide with the voltmeter?