Check the earth straps as well - there are three of them. My clocks went loopy the other week, so had a similar problem. The three straps are as follows:
1. Main strap - Battery to body to gearbox
2. Rocker cover to coil bracket
3. Body to bonnet (passenger side)
If they are split/generally knackered replace them, the main strap might just need a good clean up. The eyelet connectors easily clean up with a wire brush/fine sandpaper.
Can't say that it will definitely help, but worth checking..............
