Last night I was driving and I lost the speedometer and the
auto transmission began to shift very rough. The truck runs but there is no readout on the speedometer and shifting is a problem.

 

I changed out the blown #8 fuse and it immediately blew again. So I have a short somewhere in the wiring, my daughter said she saw a flicker like a spark beneath the glove compartment just as I lost the speedometer, any ideas what
might be causing the short?

 

Here is a valuable piece of advice I am going to give you. You need to take your rig to a transmission shop or someone with a electronic diagnostic tool for the transmission. The speed sensor in the rear axle of your rig controls 3 things the ABS, the speedo, and the transmission. I just had a custom rear axle, 9", built for my 92, I disconnected the speedsensor thinking it would only affect my ABS, which was ditched, and the speedo. I was right and had no more speedo, what i didn't realize was that sensor also tells the trans when to shift and tells the pump when you are at highway speed so it can go into full lock to pump more fluid. I blew an E40D after 10 miles on the highway and now have installed a C6 instead. A tranny shop can tell you if the speed sensor is working and if the computer is responding to the speed sensors information. Either component could give you the symptoms you are describe. You won't have much problem at low speed but you will do severe damage at highway speed. I'm living proof. Check it out soon!

 

Thanks for the information, I will be sure to avoid damage to the tranny, I onced owned a Taurus, vintage 89 and did three

tranmissions before ditching it. no fun.

 

Do any work recently to your truck? Added anything? Anything that may have shorted a wire?

 

I just had the same problem. I installed side steps and drilled through a cable on the drivers side and didnt even know it.