I went by my local car audio shop today and was talking about navigation systems... The person I usualy deal with is fairly knowledgeable, and said that for the Alpine nav unit ($2000+screen) they tap the spedometer wire, and it reads that... So, this would lead me to beleive that alpine has a rather surefire way to get the speed reading from most cars on the road today? Does anyone have access to the install manuals for their nav unit to see how they do it for most cars?

Matthew