Help with gauge cluster problem plz

[on1wheel01]

Well first I have searched and cannot find the answer. I Swapped a cluster from a 81 sr5 into my 79 base. All my research says it should be plug n play The tach does not function. I do have this black with in the pic does it need to go somewhere, I know which wire in the signal wire the single green plug, I guess I need to check for signal voltage.
When I turn the ignition on the tach needle jumps a 1/8" or so then nothing.

 

[Vicm]

That wire could be the tach service connector.
I am not sure , it has been a while since I worked on those ignitors.
If it is, there will be continuity between it and the neg terminal of the coil.
In any case if you know which is the trigger wire for the tach , then you need to connect it to the neg side of the ignition coil or your tach won't work.