I have a 1999 dodge ram 3500 5 speed 2wd dually and my speedo randomly stopped working. I towed my camper 150 miles it worked the whole way to the campsite then the truck sat for a day and a half and the speedo randomly stopped working when we went for a drive. Also just a piece of information my abs light and brake light on the dash have never worked. I checked the 40amp abs fuse and it was fine. Any ideas what it could be? Just odd it randomly stopped after sitting. Could it be the sensor on the diff or wiring going to it or could there be another abs fuse that could be it?

Oh also just to note my adrenaline isnt reading speed either so eould that make you belive it is the sensor? Cus if it was the cluster and not the sensor wouldnt the adrenaline still pick up the speed?

Check the wires/connector at the speed sensor in the differential and the wires/connector between the cab and the bed to start with.  If they are ok then then look at the abs controller.   

Ended up being the speed sensor itself, deffinetly was the original one to the truck, i pulled it out and the end of the sensor broke right off had to dig it out with a pick. The bottom of the sensor that is right by the tone ring looked almost as it had worn through some how, i stuck my finger in the hole(giggity) to feel the tone ring and all the teeth were fine and there wasnt a metal shaving shmoo on the bottom of the sensor so im just guna chock it up to 25 years and 316k miles its done its duty and signed off. Ill have to take a picture of the bottom of the sensor when i get a chance  so you guys can see how there was a little spot that was like worn through or deteriorated through, didnt look like it was rubbing though

Glad you found it.  I've heard of speed sensors going bad, but this is the first time hearing that one broke off.

It broke as i was pulling it out more than likely, it was very brittle but what gets me is the hole in the bottom like it wore through ill take a picture when i get home. And when i out the new one it it didnt work until i pulled out of the camp ground and hit like 40 mph then it came alive and been fine since