only works once in awhile

 

Vehicle details please. More information is always helpful to those wishing to provide assistance.

 

99 dodge ram van 3500,,sometimes speedometer works other time it don't,,odometer works all the time,,every other trip to town l'll look down and its working

 

Are there any fault codes or check lights on?
You might have a look at your output speed sensor, connection, wiring to see if there is damage. It's on the driver side of the transmission next to the park/neutral safety switch, they look almost identical so the one closer to the tail shaft should be the one you want.
Only a $10-$15. dollar part, worth a shot replacing if you don't see anything obvious. you can view the sensor on rockauto in the electrical section for our year and model van

http://www.rockauto.com/en/catalog/d....9l+v8,1354294

 

thank you