Tachometer Problems

[party_boy114]

Hey guys, was towing home wood last night when i noticed the tach was messed up, i was doing 120km/h and it said i was sitting at 1000RPM. I knew this was not right. thought maby a computer glitch, when i got home turned the truck off, then restarted it, the tach worked properly.
So today when i was driving it was working like it should, i went to pass a car, when i looked down the tach didn't move, got like stuck, i took my foot off the accelerator pedal, it dropped like it should, when i stepped on it again it shot up like it should, works for a bit then starts acting up again.
I replaced my alternator a month or two ago as it was shot, donno if they still run the tach off the alternator anymore?
Any Help Appreciated!!! Thanks in advance!!!!

[4ceFed]

The instrument clusters had a lot of gauge problems in 05 and 06. I would guess that you need a cluster.

[party_boy114]

Are the tachs still taken off the alternator like the old diesels used to be? Could it be a posibility that the "new" remanufactured alternator ford sold me is the problem? or would the alternator acting up not actually cause the tach needle to "freeze"? Any ideas?

[MT765]

I don't know what it could be. My dad as an 05 that just went in for a new fuel pump and now it started doing the same thing. Hasn't done it for a few days but he said the pickup didn't seem to have as much power when the tach would only read 1000 RPM. That has me thinking loose/rubbing wires somewhere. When he shuts it off though, it resets and works fine too.

The alternator was changed last year on this one so I don't know if that would be a cause. Anyone else have any ideas?