80 series Speedometer suddenly quit

[ICY80]

Was just getting back from a wet camping trip. Had gone through several waterholes and all of a sudden my Speedo started wigging out and then worked again. Next day It doesn’t work at all and lies on Zero. Been reading up on different things it could be. Just pulled my sensor off of my transfer case and split it in half to test it by putting a drill on it. Didn’t get anything out of it so I ordered one from Amazon to just try. I noticed someone before me as the current owner ran a wire from the sensor to under the firewall that looks like it may run to dash. Very confused here and could use some help. Thanks

 

[BILT4ME]

Was just getting back from a wet camping trip. Had gone through several waterholes and all of a sudden my Speedo started wigging out and then worked again. Next day It doesn’t work at all and lies on Zero. Been reading up on different things it could be. Just pulled my sensor off of my transfer case and split it in half to test it by putting a drill on it. Didn’t get anything out of it so I ordered one from Amazon to just try. I noticed someone before me as the current owner ran a wire from the sensor to under the firewall that looks like it may run to dash. Very confused here and could use some help. Thanks

What year is your truck?

It could be just wet connections. Get everything dried out (every connection and the sensor itself) and try again.

 

[ICY80]

‘97. Which connections should I check? I pulled the sensors in the front near the birfield joint grease location and I cleaned them off and the connections. No luck

 

[mudgudgeon]

My speedo stopped working because a connection on top of the transfercase had crumbled.

Sounds like you've got a bad connection somewhere and water got in

 

[BILT4ME]

‘97. Which connections should I check? I pulled the sensors in the front near the birfield joint grease location and I cleaned them off and the connections. No luck

If you pulled the ones on the front knuckles, those are for the ABS sensors, not the speedo.

The speedo sensor is on the transfer case.

it's not uncommon for this to occur.

Get out the FSM EWD and start walking through all the connections one by one, taking them apart, blowing them out, placing some dielectric grease on the seals and reassembling as you go.

 

[ICY80]

Okay. What is the FSM EWD?

 

[mudgudgeon]

Factory Service Manual

Electrical Wiring Diagram


Both can be found in the Resources section of the forum in the drop down menu

 

[Kernal]

Resources

forum.ih8mud.com

 

[ICY80]

Replaced the two piece sensor on the side of the transfer case with a new plug sensor and kept the old other plastic Gear half on and had no luck. Guess I’ll either put the old one back on or keep trying different things. Still at a standstill.

 

[xetura]

Replaced the two piece sensor on the side of the transfer case with a new plug sensor and kept the old other plastic Gear half on and had no luck. Guess I’ll either put the old one back on or keep trying different things. Still at a standstill.

I replaced the speed sensor on mine and it still didn't work. I also verified the wiring between the cluster and sensor plug was good. I took the cluster out and it had burnt traces on the back. I verified a couple weren't connected, so I soldered wire between the connections and it works now. Seems to be fairly common from my searching on here. There's pictures in my build thread.