awright folks!

having a bit of a nightmare fitting my new rev counter.

everything seems to be wired correctly and it works ok for a while but it starts to jump around like its losing the signal or something??

the instructions say

red wire to a 12v supply. i have wired it to the live from my stereo.

black wire to battery negative or to the same ground as the ignition system. i have ran this to the battery negative.

blue to one point of the terminal switch and the other side to a conveint ground(black). I have this into a brown earth behind the clocks but also had it into a black connnection behind the clocks, both which still produce the same erratic needle.

orange to the appropriate tacho pick up point. i have this connected to the green wire coming from the coil and to the multi plug fitted to the back of the clocks.

where am i going wrong??

help please?

cheers