tach goes backwards?

[wrestler20]

I bought a boat last season and have a tach that will work fine some of the time, but will somtimes sit on 1k at idle and when you open up the throttle the tach goes backwards and hits the pin at 0 rpms. Then when you slow down the needle will go back to 1k. Does anyone know why this might happen? The boat originally had a Mercury 200 on it and now has a Johnson 175 if that has anything to do with the problem. Thanks in advance.<br /><br />Steve

 

[Kenny Bush]

Re: tach goes backwards?

Better get a new tach.......controls and wire colors will differ. Buy a new tach and get a wiring diagram and check the "fire" wire for correctness......