Hi canveycat
Very few electoral registers are online before 2002. It's usually where a local archives has worked with the likes of Ancestry to put them there.
If you were in the UK, I would suggest going to the Essex Archives or British Library where they are kept.
I sometimes go to the British Library so I could instantly check the address from 1984 to his death, earlier registers have to be ordered from storage as they are not kept on site.
If you want me to look, please send the address on a personal message.
Dawn