dimming/brightening headlights

I have an 87 cabriolet GTi which had very dim instrument lights and dull headlights. The voltage regulator was testing a bit low but not majorly so. i have renewed the regulator and now have bright headlights and it appears that the switches were illuminated after all.  Question is, at idling the head lights and instrument lights dim a bit and brighten again if the throttle is blipped.  Is this normal for a golf or should I look further please?    :?

Is the alternator knackered?

I'd say alternator or battery. There again one influences the other.

Dan

This is most likely the battery voltage low. It looks as if the alternator can hold the volts up when it is at a reasonable speed. It should be putting out about 14.5 volts, if the battery volts drops down to say 11-12 volts on idle, then it might be on its way out. Cheers J.

Thanks very much for the replies everyone. I fretted over it last night and fortunately decided to go back to the supplier this morning and check I had been given the right regulator. It transpired that the nerd that served me had given me a 24 volt regulator which explained why everything was so bright. It is all ok now with the correct part though the lights were briefly awesome! I am just glad that I didn't drive it around for a week before going back. Thanks again for the advice.