Finding and connecting to the speed sensor

Your car's speed sensor sends speed information from the transmission to the speedometer. A navigation system (component or in-dash) uses this information to calculate speed and distance, and to estimate time of arrival during the course of a trip. To get this information to the navigation system, you'll have to find and make a connection to your car's speed sensor wire.

You must make secure connection to your vehicle's speed sensor to get the most accurate navigation possible. Speed sensor wire location varies; it may be under the hood, as pictured above.

Where the wire is depends on the vehicle. Sometimes it can be accessed from under the dash, sometimes from under the hood. You'll need to consult a comprehensive wiring diagram for your vehicle in order to identify it correctly. Make sure you feel comfortable with this. If not, you'll probably want to have your navigation system installed by a professional.

Using a wire tap and male disconnect is the easiest way to make the wiring connections you'll need.

The wire tap clamps on the wire you're connecting to; the male disconnect crimps onto the new wire you're connecting.

The male disconnect slides firmly onto the end of the wire tap, making a secure connection.

Once you find the wire, simply connect the navigation system's speed sensor lead to it. The easiest way is to attach a wire-tap to the car's wire and connect the navigation system's lead with a male disconnect. For an even stronger connection, you can strip away some of the jacket from the car's wire — be sure not to break the wire itself — then wrap the exposed end of the navigation system's lead around the exposed wire and solder the two together. Wrap electrical tape around the connection or use heat-shrink tubing for strength and insulation.

If the speed sensor wire is under the dash, you can run the lead to the DVD-ROM drive under the carpet on your vehicle's floor. If the wire is under the hood, you'll have to get the navigation system's lead to it through the firewall.

Preferably, you'll want to locate a hole on the firewall of your vehicle; most cars will have a predrilled hole through which some of the car's wiring already runs. If you can't find one, you'll have to find a good place to drill one — take care not to drill through a gas line or electrical wiring! We recommend that you drill your own hole only if necessary.

When running a wire from under the hood into the cab through the vehicle's firewall, we recommend you find and use a pre-existing opening, where other wires come into the vehicle cab.

Once you've found or drilled a suitable hole, run the speed sensor lead through the hole into the engine compartment, the connect it to the speed sensor wire. (If you've drilled the hole, install a rubber grommet in it to prevent damage to the lead.) Once you've made the connection, simply run the lead to the DVD-ROM drive under the vehicle's carpet.