I installed my D3 in a couple of phases over the weekend. At one point, I had the main unit connected but not the add-ons (Sirius, Bluetooth, etc.). I needed to drive my car so I quickly buttoned up the dash but hadn't yet connected the VSS or reverse sense connections.

When I was driving, I decided to check out the nav features. To my surprise, everything seemed to be working correctly, even with the VSS and reverse disconnected.

That got me to thinking ... what's the point of connecting them? What do they do? None of the handheld GPS units (Garmin, TomTom) I've used require those types of connections and they seem to work fine. Why does an in-dash unit need those connections?

The GPS accuracy seemed good without them -- it correctly showed me driving on roads and didn't freak out when I backed up for a bit. Even the vehicle speed display on the D3 was right on. Since all of this was determined by the GPS satellites alone, why are the VSS and reverse connections necessary?

Simple, the reverse wire is for if you are using a backup camera. The VSS helps keep the navigation accurate when you don't have GPS reception like in forests, bridges, downtown areas with tall buildings, ect.

Simple, the reverse wire is for if you are using a backup camera. The VSS helps keep the navigation accurate when you don't have GPS reception like in forests, bridges, downtown areas with tall buildings, ect.

Makes sense, thanks for the insight.

reverse wire is not just for backup camera but for added accuracy as well. If you put your car in reverse it produces a VSS value. Your gps doesn't know if that means you're going forward or backward unless the reverse wire's connected.

reverse wire is not just for backup camera but for added accuracy as well. If you put your car in reverse it produces a VSS value. Your gps doesn't know if that means you're going forward or backward unless the reverse wire's connected.

unless your driving a couple miles in reverse, thats not gonna matter

the vss will keep your navigation accurate. When you drive through a long tunnel or in an area with alot of trees you can lose antenna reception but the vss will still know that you are moving and will keep the navigation going. Its my understanding that if not hooked up and if the location is off it can be telling you to make a turn and you will have already passed it.