Diff lock issues

Hi guys,
My diff locks not working-its never has...only had my landy for a year or so, havent got round to fixing the diff lock cos there have been other issues...arent there always : /
Anyway Ive never worked on a diff lock in detail before so wondering if anyone could give me any links or recommend any books or manuals or anyhting..

beisde that anyone around the loughborough area can come help if you want : )

cheers guys

remove tunnel and strip , clean, lubricate reset so that it goes in ou diff lock and hi/low equally then youll know if you get stuck then ask