Speedometer, brake switch & horn-what the?

[Will L.]

So um yeah. New one on me today. A little bouncing around in the desert with my 2 boys today in the hummer.
While going up a tiny hill a funny fan against the shroud sound, but could not find anything. Then a bit later a different hill, the horn sticks on, a quick disconnect of horn wires and away we go. *FORD DISCLAIMER* The steering column is out of a ford escort or LTD2. To apply the horn you push the turn signal into the column. It is possible my sons knee could have smacked the turn signal/ horn switch.

The trans is a 4l80e, same as any 4wd pickup, using a db2 ip.

After another hour of bouncing around I took control of the rig and home we went. That is when I notice the speedometer is not working. I apply the brakes and up comes the needle to the correct speed. Let off the brake pedal and the speedo goes to zero. Every time. It is like the gauge is getting power through the brake light switch.

I will start checking out fuses and looking for kicked under dash wiring in the morning, but really have no clue where else to look. My vssb and tcm are together with connectors in good condition.

I was hoping to start figuring out other things tomorrow but what do ya do?

 

[THEFERMANATOR]

Sounds like a ground got broke off. If hitting the brakes makes the speedo work, then the brakes are backfeeding power when applied. Check to see if your brake lights are working. If they aren't then you are definately backfeeding power through the ground circuit. Or you lost a ground somewhere and the brakes sends it.