factory tach problems

[ltcbm]

I have a 86 GN that had a aftermarket tach mounted on the dash when I got it. The factory tach was still working just showing 2x the rpms. I finally got around to removing the aftermarket tach hoping it was what was throwing my oem tach off. But now the oem tach is still showing 4000 rpms at idle. Does anyone know what can be causing this? Thanks, Lee

 

[Topjimmy]

Casper's Electronics, Inc.: Boost/Tach Recalibration Svc

 

[ELLISDALLASWE4]

Make sure the two wires behind the ALT are not connected to each other..they should just be there and not connected to anything..