Charging warning light problem

Hi all, the charging warning light on my old Defender (1990 110 2.5td) is behaving a little oddly. It comes on with the ignition as normal, goes off at tickover then gets brighter with the revs going up. Battery is new and reads 13.5v at all revs so the alternator seems to be working ok. Any ideas? Thanks Marc

I'm no genius at alternator's but 13.5v is too low for long term battery health IMHO .
There are bits (diode pack) on the rear of the alternater (the cables connect to it) that you can change your self at home which may fix it.
There are smarter peeps than me on here though so hang fire till they pop up.

Battery at charge is too low, bet it's your diode pack

Quick update! I drove it today with the multimeter attached and it was rock steady at 14.3V. The warning light has started flashing though. Clearly the alternator is charging fine and there's a fault in the warning circuit.