Pelican Parts Forums - GPS Speedometer Sensor Install

http://forums.pelicanparts.com/porsche-911-technical-forum/872291-gps-speedometer-conversation.html

I was looking into a GPS sensor for my Rat Rod. There was another thread discussing them , but I thought it was best to post this here, on it’s own. There are several GPS Speedo Sensors on the market like the Intellitronix. None of them work for us as it they are not adjustable to mimic the 6,400 Pulse Per Mile (PPM) our Porsche speedometers need. So I kept searching and a unit from Autometer. It appeared to be infinitely adjustable. I read the instructions on line and thought it was worth a try. You use an adjustments button to adjust it to read dead on 80mph (while in your driveway of course, through a setting mode). It then memorizes the setting for that and you are all set.

Autometer GPS Speedo Sensor

So I ordered it and installed it……but my speedo was dead, but thanks to a friend (who had 4 sitting around) I found 1 that works. Calibrating this thing was EASY.

To install I just hooked up the power and ground the Autometer unit needs to the power and ground that plugs onto the back of the gauge. The signal wire for from the Autometer “brain” REPLACES the signal from the tranny sensor. I stuck the antenna under the dash pad. It is magnetic, so I just stuck it to the dash board metal in where the speaker would go (1975 with center dash speaker). It needs to have a clear view of the sky (meaning no metal on top of it) and it can shoot through plastic/fiberglass/etc. Once hooked up you press and hold the calibration button until the needle rises close to (but below) 80mph. At this point you press the button to make the needle rise a little until it is dead on 80 mph. Once there wait 5 seconds, the needle will drop to zero and you are calibrated. I had to do it twice, the first time I had the speedo in my hand. Once in the dash I realized the angle to my eyes as I drive was different. So I recalibrated it while it was in the dash and I was in my driving position and it is now dead on.

The one catch is with key-on power the speedo doesn't read until the unit gets a GPS fix, which takes a few minutes if the car was off over night. You can hook its power to the battery for a faster fix (obviously this causes some drain, but it is minimal).

Obviously in a long tunnel or parking garage it will lose its signal. The longer I have had to wait though is about 2 in. No big deal. I am VERY happy with this though. I put a new sensor on my tranny and ran new wires, but that did not work. Now that I have realized my speedo was dead, maybe the sensor did work, maybe not. Regardless, now I have a GPS system that can be adjusted for any tire size changes. The install was literally 30 minutes, and the calibration took 2 minutes.