I have an extractor fan in the bathroom.

It is controlled both by a humidistat (separate, not built in) and also
by a ceiling pull switch for manual operation. Supply splits to feed
both of these, then runs to the fan where they terminate at the same
point. Problem is if the fan is on I don't know if it has been turned on
and left on or if the humidistat has switched on. So an indicator would
be useful.

I tried a neon indicator in the switch but this doesn't work - it
light's up if the humdistat turns on anyway - I guess because there is a
current flowing back down towards the switch.

Suggestions as too how can I arrange things so the indicator light on
lights when it is switched manually would be welcome.
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Chris French, Leeds