Check the earth connections.
My 4/4 - 1992 CVH was the same. A good clean of the connections cured it.
As a test, try connecting the neg battery terminal to a mounting bolt for the starter. This bypasses the earth connections that may be at fault. If the car turns over ok then it's one of the earth connections. You can clean the connections/renew the straps to solve it.
I used a jump lead on mine but BE CAREFUL, connect to starter bolt first then battery! Luckily the jump lead is long enought to reach from battery to engine.
For a few days I carried the jump lead "just in case", until i sorted the earths.
