Tachographs are either mechanical or digital. Unlikely that you have a digital tachograph. A mechanical one (i.e. all the old ones) is driven by a flexible drive cable from an adaptor on the rear of the gearbox. Jump starting and 24 V won't have any effect on that. However if the drive cable snaps due to fatigue (which can easily happen) then the tachograph will read zero and the odometer ("mile-ometer") won't change. You need to get a new drive cable - easily done - they can usually use the original sheath and end fittings and just make up a new cable for you).
Which needle are you referring to? The stylus that marks the chart or the speedometer needle indicating your road speed?
There is a fuse for the speedometer/tachograph (fuse no. 15 - 10 Amp - if you have a 3 piece instrument panel). The fuse box is on the passenger side under the glove compartment. It is covered by a black plastic cover which is held in place by 2 plastic screws/buttons.
JD
November 2009