I just bought a 2003 honda forman 400 4x4 and the speedometer does not work.it lights up do you know what the probm might be

Not sure why but Honda in their infinite wisdom integrated the 4WD among other functions into the speedometer on a few years. If your speedometer doesn't work either chances are you need a new speedometer. At like $400! It is what happened to mine. If you start run the engine at all with a dead battery (hand start, jump etc.) it WILL fry the speedo, the 4WD the reverse bypass, etc. I learned the hard way.

The brightness for the instrument cluster is adjusted by pushing the knob at the lower left of the speedometer. See page 77 of the online owner's manual Here: http://techinfo.honda.com/rjanisis/pubs/OM/AH/AE10303OM/enu/E10303OM.pdf

could be speed sensor. the light is on because the trans doenst know the vehicle speed.

did you check your fuses???

the speedo could be the sensor on the gearbox the lights not working could be the bulbs have blown

I had the same problem on 1991 Honda Accord! It was the old AT fluid. I changed the fluid and all problems vanished! I had asked a Honda mechanic at first problem and he said make sure the AT fluid is good! Happy Honda Owner