hi
as you say make sure all the earths are 100% ..espically the batt earth to the chassis ,remove clean to bright metal refit ,.the engine earth ,if xe engine with upec,i think earth is on o/s on the bellhousing .if i remember correctly there is a fresh hole next to the one used that you can screw in to ...and not forgetting the good old starter ...
will admit in 15 years with DAF haven't ever heard of that fault .so wouldn't say it was common..you mention you had it at foden and they weren't interested ,don't you have a local DAF dealer ???...you could run fresh 4 core wire from the bulk head to the tacho ..hope you didn't renew the box because of the fault ...but start with the earths ...and then see hoe it goes
norb
February 2011