[stangman96]

the reason you needles move to the max (its called a sweep or self test) is most likely you tapped the wrong wire for power, i am not sure u sould have the power on the cig supply, it should be ignition only, so it is powered when key is on.. electrical add on cause havoc on all the rest of the electronics, hence your needle sweep, these cars are using multi-plex communications, in other words, modules "talk" to one another for info, speedo is considered the HEC module, or hybrid electronic cluster module, fords fancy way of a speedo with a brain. hope this helps you and you get your bug worked out...