ACE shift lights fitting 310R

[Tartanbj]

Hi

Ive been trying to fit the Ace shift lights to 310R

I found the right 3 pin connector under dash to right of dials but when I fit the lead from ACE control box I get no reading on Revs from engine and the Rev counter on dash stops working.  Clearly the power is working as I get the 3 question marks on digital read out but no rev reading. 

Anyone had similar challenges and found a solution. Don't want to splice into existing cables when there is a connector that's supposed to to the job. 
cheers

Bruce