I noticed the other day that when I switched on my headlights, there was a discharge on my Rover's ammeter. It self corrected after maybe one minute or so. Without the headlights on, the ammeter needle would sit at the null position whilst driving, but I suspected something was in need of attention. So today I switched on the headlights again, and again a discharge, except this time there was no self correction. So, I surmised that one of the brushes was likely in need of replacement, and upon inspection, that is exactly what I found. The brush closest to the bridge rectifier makes contact with the slip ring at a distance from the centre, whereas the brush closest to the voltage regulator, makes contact with the slip ring at its centre. It is the former brush that was in need of replacement. The voltage regulator in on the left, the bridge rectifier on the right. The two brushes reside within the brush box, atop the slip ring. The shorter brush is 7mm in length, thus in need of replacement. The stated minimum allowable length for replacement is 8mm. The longer brush is 12.5mm in length. When new, the brushes are 13.0mm in length. I use Cargo brand replacements. The voltage regulator of the same brand has proven to be extremely reliable. After replacing the outer brush, subsequent testing showed a successful outcome. The culprit was indeed the worn brush! Ron.