I think that this is what Tim referred to, taken from a French dealer document in the early 70's:
ALLEZ LANCIA
Lancia France Network - Information Bulletin
Number 76 26th Jan 1970
Workshop note
Subject: Flavia Berline 819 - fitted with alternator
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You may notice under certain conditions, and especially whilst driving at night, a slight glowing of the alternator charge light.
This slight glow is not, as one may think, a charging fault. In order to avoid this inconvenience, we advise you to replace the 3w dash warning bulb with a 4w bulb