my 95 300tdi manual just has the one wire to the back of the pump and it will easily do 30 mpg an i am tight arsed mechanic an keep a close eye on its consumption best is 35 on a run up the m1 at 55 mph from junct 29 to 36. only reason i got the disco was cos its better on fuel an cheaper to run than the paj i had before.
Not goin to be as good as the Isuzu then, I got 47 mpg towing a twin axled trailer 150 miles to collect an axle and two gearboxes, that's at 55 mph and the truck the engine was in was a bit lower than a Disco so les drag.