I just ran into this myself. I have a FEDERAL 84 TD, and its tachometer is attached to an "engine speed sensor" that is bolted to the engine where it meets the transmission. Your 83 does not have the mount point or the sensor, and gets its signal from the TDC sensor on the harmonic balancer through the amplifier plugged into the diagnostics plug attached to the left fender. I don't know if the signal from the 84's sensor is different from the 83.
My car has an earlier engine installed and so I have a dead tach as well. I'll try to brew something up in the spring that will allow the TDC sensor to drive the 84 tachometer. You may want to take the cluster back and see if you can get an 83 version or earlier...
Here's a link to that thread:
Figured out why my Tach won't work...