My speedometer abruptly stopped working. This happened once before, both times it has been associated with driving in the snow. The first time, it bounced off and on then resolved over a day. This time it just quit flat. I looked under the truck at the sensor connection on the rear axle nothing looks amiss (no ball of ice on the connection).

Here's the complication. This occured immediately after I wired my exhaust brake to a new shifter mounted switch. This is relay controlled and all connections are intact and working appropriately. I did not tap into anything that should affect the speedo. I'm using a Painless Wiring fuseblock tied into the battery and cigar lighter for accessary connection. It's probably just a coincidence I don't think the new switch has anything to do with it. Of note, the exhaust brake won't operate because the speedometer is reading below 15 mph (zero).

I checked the fuses, nothing there. I didn't check them all, none are labeled as speedo, guages, etc. Is there another place to check?

 

FWIW, I parked the truck in the shop and thawed it out. The speedometer started working right away (as did the E-brake).

It must be getting wet somewhere, any ideas?