Outer Limits 4x4 Board

any info would be appreciated guys. on a td42 were is the tacho sender located? mine is a dx so i assume its not fitted from factory and id like to get a sender and rig one up. so any info about this ie were there located how they work etc woul be great.
thanks guys
matt.

just beside the water pump on the right side like a lil black oval cap with some wires stickin out if you have it fitted.

much appreciated
cheers dude
matt