sr swap tach doesn't work

[1bad91s13]

just finishing up my sr swap and it runs and all but the tach doesn't work. I have an early 91 s13 . I've read that the single cam tachs don't work with sr's I have a 91 but it was made in 90 could I have the early cluster? I tested the signal on the yellow/red wire and I get around 6volts with the key on and 6 volts when running. My tach worked before the swap. Any help would be greatly appriciated

[compactfean]

If you had a single cam motor than you had. A single cam gauge cluster. Which wont work. Plus voltage is not how the tach works....it works off of a square wave signal.