After serious thinking Steve wrote :
hi,
Fiat Punto 1.2 petrol w reg year 2000 has apparent varying light brightness
to headlights and interior lights.
when stationary and rev engine lights tend to brighten then dim. this applies
also to interior lights. When driving along the road in darkness, the lights
tend to vary in brightness.
any ideas ?
Steve for a friend.

If the alternator is under a heavy load, the voltage will drop a bit at
tick over and the lights dim a little. If at normal road speeds they
are varying, there is a fault on the alternator which needs to be
checked out - it could mean a rectifier has failed or the voltage
regulator.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk