You thought correctly...Higgs Boson: 1998 Land Rover Disco...my thinking then is perhaps the cruise con is the interrupt....or perhaps does not need the continuity in speed out...as with most things British...enigmatic as to why they chose to make such a beautiful mechanical truck poisoned by electronics...

 

how is the battery and the charging system? And is the vehicle's belt installed correctly.

 

Update: Turns out it was a bad relay...aftermarket relay that was shorting out and not conveying info to cluster.

 

What an expensive relay that proved to be!