Electrics and engine cuts out for a couple of seconds.

Hi I’ve got a 300tdi defender 90 it’s lights and dashboard lights are like surging normal then dim and intermittent the engine cuts out can be a split second and back as normal or a couple of seconds its normally on low revs (eg coming down the gears) I’ve checked the earth cable and cleaned the connections up. It’s just doing my head in now.

Have you made sure the earth from engine block to chassis is Good?