The speedometer is not working but the other guages are for my pontiac montana 2000

Sounds like a broken wire on the - side.

Is your fuel gauge not working?

Replace the fuel sending unit it is in the tank. I would check the voltage going to the guage first make sure you have 12 volts at the unit.

Yes

The sending units fail in these vans. Have it replaced, I always suggest replacing the fuel pump and sending unit as a complete unit.

It gets a little complicated here but I will tell you what it can be. Devective dash voltage regulator, lost ground at sending unit, break in wire going to the dash, bad sending unit. Check the fuse, may fix it. Other then that, you will have to check these parts. If you have another question, write me back. I will help the best I can. Thanks for choosing FixYa.

It is most likely the speed sensor in the transmission.

inside the door panel for the module ,speedo lights and fuel gauge is another problem

From 2003 to 2006 GM - chevy , pontiac , buick , cadillac , had bad step motors inside the instrument clusters , causing gauges to no work or sporadically . Happened to my 2005 chevy cavalier , went to automotive salvage yard ,got a used one for $20.00 buck's . That was two year's ago , now problems !
How to repair GM Instrument Cluster Speedometer Gauge Stepper
Or you can buy the up graded stepper motors on eBay an fix it .