Hello!

I have scorpio ym. 1990 and i have trouble getting the speedometer to work. Originally it was 2.0i dohc with manual gearbox and i have planted 2.9i 24v(bob) cosworth engine there with a manual gearbox. The speedometer worked fine before the mods aswell as the sparecar from which i took the manual v6 box had a working speedo.

This much has happened:
I have broken atleast the speedometer because i didnt know how to wire it. I was testing it and put +12v to the speedo wire and after that fuse blew and speedo was lifeless. I took it a shop that specializes in repairing these things but so far i havent had success in getting it any movement.
I have tried 3 different speed sensors with no success they have yellow, black and brown wire. Supposedly yellow is + and brown is ground and black is signal but all the sensors give me different readings (readings alternating voltage) when i spin them in a drill.
Now i have tried different wiring setups for all the sensors so i may very well have broken all the sensors too...
All the sensors give readings between 0V-3V none give 5V and thats what i thought they should and another thing is that if these sensors work like i think they should have 0V when its not turning but all the sensors i have show atleast 0.3-1V at all times.

Could anyone please clarify following for me:
Sensor wiring:
Yellow = +12v
Brown = ground
Black = Signal

and what readings should i get when i test these sensors?

Thanks for the help in advance