I was hoping mabye someone has seen the following problem. Just yesterday my speedometer stopped working and the overdrive "off" light on the end of the shift lever started to flash. I shut the truck off and back on and everything was back to normal. Now it seems like every other time I start the truck the problem is back. What I mean is that if the problem starts again I shut the truck off and restart it and it's gone. But next time I start it the speedo doesn't work and the overdrive off light will start to flash. I looked in the owners manual but couldn't find anything about a speedometer relay. I've never seen this before but to me it seems like a relay is getting ready to go bad. When the speedometer stops working everything else works fine, including the tachometer. The only other indication is that the overdrive light flashes. Thanks for any input in helping me solve this problem. 99 f350 SD PSD

 

It's probably the VSS. That's the little speed sensor on the top of the rear diff. housing. It's around $20 from the dealer and takes about 10 min. to change.

 

Thanks for the feedback. I got the part from the dealer and will crawl under the truck tomorrow But looking at the part it looks like cake to change. Thanks again!