i have a 2000 ws6 standerd. having issues with the tachometer. sometimes it wont work(the needle dont move at all) useally when im on 4th gear and 5th gear the needle goes dead and drops,then it will go back up and work fine and in a little while it will go dead again. can any one tell whats causing this and how to fix it. my car runs fine,just having issues with that. thanks (hope that makes sense)

 

Anybody?

 

This could be the first signal that your alternator is on its last legs. What does your voltage gauge do when this happens? Does it drop below 13V?

 

the voltage gauge does not drop below 13v, it stays on 13v. i did change alternater a couple of months ago(3 or 4 months ago). i will check again thou, but could it be something else?

 

It could be a broken wire or something like that.

Did you install a reman alternator?

 

the tachometer inside the instrument panel cluster (IPC) gets all it's information from the PCM, it's referred to as class II serial data. There is not a single tach wire coming to the IPC that could be broken. The PCM knows what the engine rpm is via the crank position sensor (and maybe cam position sensor) and then it tells the IPC what the rpm is to display on the analog tach gauge. So if this data link was faulty you would know, because the engine would not run fine and you said it does.
The service procedure is to install a scan tool and connect to the IPC and check for diagnostic trouble codes (DTC's), this can only be done at the dealer with their scan tool. They can also command just the tachometer to sweep from minimum to maximum to verify it works. What comes to mind is the stepper motor that makes the tach needle move, I just bought a 2006 GMC truck which has a very noisy IPC, sounds like little motors with dry roller bearings spinning in there when you turn the ignition on. Do a google on GM stepper motor recall, I don't think the F-body's from 1998-2002 were affected but for my truck I can buy 5 or 6 replacement stepper motors for about $50, crack my IPC open and solder in new steppers rather than replacing the entire IPC for a few hundred plus dealer program. If the dealer diagnoses your problem as a bad IPC, then they will just tell you the whole IPC needs replacing- whether or not you can replace the stepper motor I don't know i believe they are all the same and you can buy just one which is the updated non-defective kind off amazon or ebay for less than $10. That's if it is just the stepper motor on the tach, it could also be something else where you do need to buy a whole new IPC, with everything off and quiet put your ear as close to the IPC as possible and turn ignition key on. do you hear any spin up noises in the cluster, if so then that's a good sign it may just be bad stepper motor. if it's completely quiet then it may be a bad solder joint or something in the IPC. good luck, in any case a new IPC would most likely fix it but that's expensive.