SR Swapped S13 no tach works

[MyblackS13]

I have an 89 240 with an early redtop SR20DET and I can't get any tach to work. I've tried the dohc tach, s13 180sx tach, and a defi tach, none have worked. Every other gauge and idiot light in the car works right. The more I work on it the more confusing it gets. :bash:

[SirWarrior]

is the second plug by the ECU plugged in??????
I think its brown and ECU is blue IIRC

[projectRDM]

Tach is yellow/red. Make sure it's connected.

[MyblackS13]

ok...here's an update, I've tried a KA24DE tach also...the dash harness is hooked up and I double checked the wires making sure the tach signal goes to the same yellow/red its correct. I've checked it with a multimeter on the a/c setting and I'm getting the same voltage readings at all points along the wire and it goes up with more throttle, so I'm pretty sure I'm getting a signal....unless its weakened for some reason. I believe I was getting about a 6.5-7.5vac on I believe a 200mah setting on the meter (I'm not totally sure about the settings since I'm not extremely familiar with multimeters and writing from my memory). With moderate throttle application it increased to about 12-13vac. Anyways...now I am at a total loss. Either I've installed 3 bad tachometers, the signal is weak or I'm totally overlooking something.

[the head]

1. cars run on DC not AC so that may be part of it

2. if look for any brakes in the trace (metal path on back of gauge cluster) for the tach

3. was power/ground hooked up with the signal

4. what else is on the fuse for the tach? does everything else on that circut work?