tacho working intermitently

[Sylvester]

Hi guys my tacho is playing up a lot lately ,when I hit the dash with my fist or I go over a big bump it springs back in or out of action reading the correct revs ,
ive tried cleaning the plug by the injector pump and the plugs going in to the back of the instrument panel , is there anything else i should check , was wonder if i should pull the instrument panel apart next .

[geeves]

rob mentioned a similar problem a while back but on the earlier 2.8. the loom was shorting out under the pump