weird intermittent charging problem- mrk6 RWD 2.4

[Jebjem]

Wondering if anyone's seen this before...battery warning light goes off after engine fires up but comes on again 20 secs later & then stays on apart from a regular
off every minute or so, with the idle revs & hdlamp brightness dropping momentarily at same time. Seems maybe the alt is kicking- in & out. Belt in fair condition & not slipping, all fuses OK, batt & alt connections seem OK. Could it be a relay & if so how do I test them? Or am I likely needing a new alt?
Mrk 6, 54 plate, 2.4 RWD, SWB panel van.

[amlav]

Could be the alternator brushes wearing out or a bad/corroded contact somewhere .

[andz327]

You can buy alternator repair kit , the brushes and voltage regulator come as a unit for around 20quid and easy to replace but it could be your alternator pulley, if it's similar to the mk7 as they have a clutch drive mechanism in the pulley and it maybe spinning freely and only catching now and again