some days when im driving my '96 mustang, the speedometer and tachometer tend to stay at 0 while im dirving, this mostly happens to the speedometer but sometimes to tachometer too.

this usually happens on cold days, as l am from colorado. But usually to fix it, l have to hit the window case that holds all the guages and then the needle goes up to the correct speed.

sometimes also when l accelerate fast, the speedometer needle zooms up to about 60 - 70 mph when im only going about 30 or 40.

what do l need to do to fix this problem? thanks :)

Your car need critical tests that us in the UK call an MOT.

This could save your life, what your doing otherwise is a dangerous thing.

http://en.wikipedia.org/wiki/Vehicle_inspection

this is a common problem in almost any vehicle as it gets older. It could be anything from a loose connection to the speedometer, or a speed sensor problem.

You could fix it easily enough, but why? Just ditch the Ford and get a 69 Bus. Life is nice at 45 mph.

l drive a '98 dodge neon & the exact same thing happens. But mines usually does that in any kind of weather. l am trying to figure out how to fix mines too. l have not had it fixed yet because l have not had time.
These MIGHT be two solutions:
1. My mom said there might be something wrong with the fuse? ( l do not know too much about that)
2. My cousin is car does the same thing also. She said that somebody told her to drive the car in reverse. Then put it in drive & it should return to normal. ( l do not know too much about that either) :)

check you vss(vehicle speed sensor) on the side of the trans. There is a tooth driven gear in there and it might be chewed up and not working right. Its like $5 from ford IF that is what it is. Does not hurt to check that.