Changing cylinder head gasket(help)

May have solved problem ( ?) ...checking earlier on the back of alternator on the d+ there was a black wire ( always been there since I've had it , not a factory fitted one) that leads from d+ through engine to a large relay situated just behind alarm horn . Unscrewed nut on d+ removed black wire replaced nut , started engine and hay presto battery light has gone out , don't know what black wire was/is for however not attached to alternator any more . Will check everything works later . Just seem odd that the black wire has always been there and only just caused problem in last few days . I still keep in contact with the bloke I bought Landy off so might give him a bell to see if he can shed light on the black wire .
Just hope I haven't " hidden " another problem by doing this .