ZX Diesel rev counter

My wife's 1.9D rev counter occassional drops and then recovers, sometimes to half revs and then back to full. Before I dig out the
Haynes BoL any clues as to where the connectors are?
It's not an urgent problem, we rarely need to take it above 3k revs except just before an MOT.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.