I have a 93' tacoma 4wd. When riding down the road the speedometer will go to zero and back up to the speed i was traveling over and over again and ever time it does it the radio will turn on and off. I think its a bad ground, and if that is the case I need to know where all the ground points are on the truck.

 

download an FSM for your truck...it will be your best resource.
Probably corrosion on your main hot lead(positive)...not at the terminal but inside the wire. It's possible the line is corroded, and creating resistance=bad.
If neglected, your truck will stop running, and will not start.
these are things i would check ASAP.
this is based on the limited info you have provided.


does the truck actually die? do you have a Tach? does that also go to zero? Does it do this under load(foot on pedal) or coasting?

If you live where it is humid, corrosion could be the issue. Could also be a loose ground, but you will need the service manual for that.

 

Thank you!