Dangerous Issue! Mercury Marine auto pilot suddenly turning off while underway

While out on the boat the Mercury SmartCraft GPS300 3.6SC GPS Antenna was suddenly losing its Fix causing no signal to come to the SmartCraft VesselView display. 

Once the SmartCraft VesselView does not receive a GPS signal the autopilot no longer knows where the boat is headed and pointed so the autopilot automatically goes into standby mode.  

On any vessel this occurs it can be very dangerous for several reasons and needs to be addressed as soon as possible.

So we used the autopilot for the rest of the trip only under the knowledge that it could turn off at anytime, so whomever was at the helm had to be ready for it to occur and keep a constant watch on it.

Once back at the dock the Mercury Marine GPS unit was located on the top of the hard top of the Sea Ray 500 Sundancer express cruiser just forward of the radar arch and in the middle between the overhead power sliding windows on the Sea Ray.

To find out how the cable was run I first unscrewed the Mercury Marine GPS 300 from the mounted pole.  The cable runs up into the GPS unit plugs in and then the metal nut screws on to secure the unit.

Remove the three screws holding the top of the GPS unit to the bottom pole mount adapter.

Once those three screws are removed you can now see the metal thumb bolt that secures the cable to the Mercury GPS300 receiver.

Remove the metal nut from the threaded pipe on the GPS unit. Be careful to secure the cable with some electrical tape where it exits the 1″ pipe so the cable does not fall into the hard top.  If the cable were to slip into the hardtop opening this will create a bigger project than you anticipated.

After the unit is removed you can remotely bench test the GPS unit to make sure the unit is what is not working properly.  If the GPS unit is working properly the issue may be the cable leading to the unit, the SmartCraft VesselView is causing the issue or the autopilot function on the helm pad controller is not working properly.

This unit was found to be not working properly so I ordered a new unit.

Information regarding the Mercury GPS 300 for the Smart Craft Vessel View Display and autopilot. 
Mercury GPS300 3.6Sc Antenna
Associated Part Nos: 8M6002178, 8M0079126, 8M6000911
1″ pipe w/14 threads per inch for Standard Marine Mount
New In Box
Mercury Outboard Rigging Parts, Controls & Gauges Joystick Piloting Systems Zeus 2.2/2.5 SmartCraft Rigging IMU and Component -Design IIMU and GPS (Design I)

I was able to locate the new Mercury GPS300 3.6Sc Antenna with associated Part numbers 8M6002178, 8M0079126, and 8M6000911 at a few dealers.  But fewer and fewer are in stock every month the known inventory of them is depleting. 

This unit is becoming more difficult to find but you can still get it directly from FP Marine at the website link below.

https://www.searay-parts.com/Mercury-SmartCraft-GPS300-3-6SC-GPS-Antenna-p/mercurygps8m0079126.htm

FP Marine/Sea Ray- Parts.com
255 Barnes Blvd.
Rockledge, FL 32955
ph 321-639-2951
fax 321-639-2953
email: sales@SeaRay-Parts.com

Unfortunately these parts may eventually run out, but for now there are some in select inventories around the country and internationally.  But if you have issues buying a new one from a Mercury parts dealer you can find new and used ones on ebay as well.

Mercury GPS300 3.6SC has been superseded by the newer version of the unit which has a part number of 8M0091565 – Antenna GPS400.

So it seems that Mercury Marine has stopped making the GPS300 model.  So in the future a used unit from ebay or other parts store may be your only hope. 

The new model from Mercury the GPS 400 may not connect directly to the existing cable leading to the other electronics.  I will have to try confirm if the cable connection is the same.  If it is not the same you may have to replace the cable leading to the Smart Craft Vessel View control panel and autopilot controls. 

Update :  Mercury – Mercruiser 8M0091565 Smart Craft GPS antenna 400 has indeed replaced the GPS 300 but is listed as the new superceded part but is a functional replacement but may look different form the original part.  I have not however been able to confirm if the cable connection into the unit is compatible with the cable end that connected into the GPS 300.

These units are primarily used in the Zeus SmartCraft rigging.

_______________________________________________________________

More information on the GPS400 part Below:

8M0091565 SmartCraft GPS Antenna 400

SmartCraft GPS Antenna (4.0.12SC) Used with SmartTow Pro SC1000 gauges,
MercMonitors, and VesselViews 4 and 7. 

Sends CAN H and CAN P GPS data for use with GPS SmartTow and Joystick
Piloting boats with Auto Pilot. Software 4.0.12SC 

Part number 8M6002178 includes everything below within the package.  Below is an image of all parts in the pink plastic bag.

Main part number included in this package is 8M6000911 which is the GPS300 GPS antenna receiver.  Along with a new base that can screw onto a 1″ mount, new screws, and some supporting document papers.  (Pictures of the paper pages below).

Mounting the new GPS feed the cable through the new base that screws onto the one inch pole.  Once cable is through screw the base onto the pole.  Then attach the cable the GPS 300 receiver.  Finally use the supplied three screws and lock washers to attach the GPS receiver to the base.

Everything installed and in place on the hard top.  Next step is to check to see if everything is working properly at the helm, SmartCraft Vessel View, and Precision Autopilot control panel.

Everything is working perfect with the Mercury Precision Pilot control Panel (where the autopilot function, and sky hook buttons are located), the Smart Craft Vessel View (where is shows the knots or MPH of the vessel), and the Joystick controller are all working perfect now.

New

I always like to see what is inside the old unit that is no longer working and like to see if I can find a way to fix it or if it is truly completely gone.  Either way its interesting to see what little is actually inside some of these boat parts.