Speed Sensor
 

where is the speed sensor or sending unit that send the signal to the speedo?

Driver side fire wall.

good tip, repair manuals help :P trust me.

i had a haynes manual b4 but i cant find it

Haynes makes a good manual

any detailed info?
which one is the signal wire, and where exactly is the sensor?

It should be coming through the firewall directly behind the instrument panel, or in a bundle from the same area. Hard to say without looking under the hood, but should be fairly obvious.