My tachometer is stuck at 1000 rpm , doesn't move at all, before this it was simply never reading correctly . Is there a fix or should I just replace it and if replacement is best, where can I find one?
sure it is stuck at 1000, not 500rpm?
(there is a pin the needle rests on, at 500rpm)
you can't just buy one (well, unless someone has a NOS unit hanging about!), but they can be repaired.
First check the brown/white wire on the coil minus, make sure it is clean and tight (remove, clean, refit)
If that is OK follow this wire along the inner fender to connector G133b (see photo) unplug this and clean with a little contact cleaner, refit. From here it's a white wire which joins up at the tacho behind the instrument cluster. To check there you'll need to remove the whole 'monopod', no big deal when you know how.
If all these connections are OK, then the fault lies within the instrument itself, and it needs to be sent away.