Got a strange one here. My 7.3's speedo started bouncing around about 6 months ago, mainly when I hit a bump. Then stopped working altogether. Occassionally would come back on but bounce once again. I replaced my VSS and wiring harness on the rear differential. I butt spliced the harness to existing wiring. No dice, speedo still didn't work so I thought it was something else. Been dealing with this for 6 months determined to figure it out. I finally figured out (light bulb went on!!) that when the truck got wet the speedo worked...(Desert rain occasionally and washing it). Turns out that when the butt splice itself gets wet, not the sensor, the speedo works perfectly. Once it dries out, speedo stops working again. I dump a cup of water on the splice and speedo works yet again. I used heavy duty butt splices. Is there a resistance issue or something similiar going on that the water fixes?