Can a GPS speedometer be hooked up to an exsiting GPS unit or do you have to buy the seperate GPS sensor?
A Gaffrig GPS speedo cost about $200 and the sensor cost about the same. Is it really worth $400 for a speedometer?
What do y'all think?

Or you could go with a Nordskog and knock off about a hun.

Here is a link to a thread on this subject.

GPS Speedos

Good luck.

I hooked mine up to my garmin unit and it works fine, You would hook the wire from the sppedo to the "NEMA" output on the GPS. Also both ground for the GPS receiver and the spedo head should be the same too. Some gps's have different settings for this output wire for other equipment, You may have to go in the setup screens to choose NEMA. but I believe the NEMA standard is 4800bps and that is what the GPS speedo use's for data.

I had mine hooked up this way first then I changed back to the full time receiver. My problem was I had to turn on the switch to the Garmin unit and the hold the on button first before it would start to accuire and show MPH. I had bought the whole kit and had the second reciever anyhow.

Garmin has OEM Sensors and the GPS35 is what Gaffrig Perf uses: http://www.garmin.com/oem/

Here is the instruction sheet: http://www.garmin.com/manuals/spec35.pdf

I think I bough one a year ago for a motorhome for about $135.00 from a wholesailer. You could also use the GPS36, it is the same but on a pole and white for marine.

You would use the Black, Red and white wires only. White would go the the GPS Input.

Here is a pict: my existing Garmin gps reciever is on the pole abover the walk way, the "new" one (Garmin from gaffrig) for the speedo I mounted just abouve the trim indicators. They only came in black so I had painted it to match with automotive paint, I just drilled one hole and used sticky tape to hopld it down for now to verify that it worked there. It seems to be fine, If the tape goes bad I will just calk it down.

Be carefull painting GPS antennas, especially white. Most paints these days have metal in them, titanium oxide in whites, which can kill the antenna reception. Be sure to paint a test piece of plastic first and place it over the antenna to be sure it doesn't obstruct the signal.

-Greg

I have to ask this, it has been driving me crazy! Why buy a GPS speedometer??? These things cost $400 to $500 and all they do is read out the speed. For the same money or less you can buy a GPS unit from Garmin, Magillian, etc that not only will give you speed but also give you max speed, avg speed trip miles and navigation info. For just a few dollars more you get charts. Am I missing something here?

Yes they will do all that but I had mine mounted down lower and It was hard to read. Where the center guage is it is less destraction from the view ahead. Some of the GPS's you can move the data fields arround and make the numbers bigger.

As for at the paint I used Duplicolor arctic white, it seems to work fine.

I agree, a "speed only" unit is somewhat of a waste. I have a full mapping GPS with depth on the Nav panel, and run a remote display head to the drivers panel for the speed readout. Cost for the remote head was only $100, and now I don't keep tearing up speedo pitots all the time. I do however miss the "extra speed" of the water speedo .

-Greg

I already had a gps hand held. I wanted to get the gps speedo because it would be easier to read. I hooked the speedo up to the unit using a patch cable, but finding a cable with both signal output AND power was extreamly difficult. In retrospect it's not worth the trouble and I should have just spent the money for the antenna.

GPS speedos don't really cost much more (if any) than a high quality conventional speedo. If you buy a liquid Gaffrig it will cost at the very least something over $200.00 just for the head. Add another 200 (of more) for a spring loaded pitot and hose and you could have bought a GPS unit for about the same money. Of course you can spend less but you won't get the same quality or accuracy either. My next speedo will be a GPS because I want to get rid of the pitot and I like the ability to read slow speeds which is lacking on the 100 MPH and up conventionals.

Oh, and don't forget the aesthetics of having a matching gauge in the middle of your dash versus a GPS unit stuck up there somewhere . . .