FOAK current problems 2.5td

My 90 has recently developed a current problem - as in electrical - there are always other little problems... The little red charging light comes on intermittently and when it does the voltmeter needle drops down into nearly the red, I think this is normal in the sense that it is correctly showing me a problem, but what can it be? Why is it intermittent? Bad contacts somewhere? I have a feeling that this started fairly soon after me leaving the headlights on and draining the battery. I just jump started the thing and went for a run, started fine next morning. The other niggling thing is the brake warning light on the dashboard also comes on and off at about the same times as the charging light could these be linked? I checked the brake fluid level and it is slightly above the minimum mark, is it just missing fluid or could it be more serious? puzzled... TIA tony