Cutting dash for flush mount Garmin 431s

If you are handy with a checkbook, you will get alot done :D
 
Following are detailed instructions written by JCinNC.  I copied and pasted the following for others to search and find have detailed instructions on installing a GPS.  JCinNC wrote:

Very easy install.

 

You don't need to order the kit (the Lowrance uses M3 screws and these can be bought at Lowes or another home improvement stores  I purchased the M3-20 screws (x4) and #6 fender washers + a washer to create a countersunk area for the head of the screw.  Lowes has it all in their specialty bins and stainless screw area.  Cost me less than $2-$3

 

Sorry no photographs but very simple to do so they weren't needed.

 

Make sure you ACC switch is off or if you want, disconnect the battery (I did not disconnect mine)

 

1.) Under the helm unplug the Echo power and transducer wires

2.) Remove the 4 nuts and washers holding the dash insert (not the echo, the entire dash insert)

3.) With the dash insert out remove the wing nuts holding the Echo in place and then remove the threaded rods

4.) Tape template onto dash insert (note that the four holes for the flush mount will possibly be on a side surface where the insert is molded.  It is not an issue but you may have to make the mounting hole slightly larger later.

5.) I marked all of the center drill spots with an awl to make it easier

6.) Using 9/64 bit drill 4 outer holes as marked for the flush mounting option.  Using the same bit go ahead an pre-drill the other 4 holes to so that you have a pilot hole

7.) Using a paddle bit, drill the 4 inner holes using the pilot holes created in #6 above

8.) Draw straight lines tangent to the four large holes you just drilled to create a rectangular opening for the Lowrance. (note: my Echo opening was slightly higher than the top two holes but was completely covered when I installed the Lowrance)

9,) With a jigsaw, cut out the square you just made.  Use a hand file or orbital sander to smooth out the edges.

10.) Place a towel on a table or workbench and place the Lowrance face down.

11.) Install the (4) m3-20 screws, fender washers, and other spacer items you may be using into the 4 brass helicoils in the corners.

12.) Snip the power wires going to the Garmin above the fuse.  We will leave it in place and use it to install the Lowrance.  This also made it easier as I didn't have to do any work on the white plastice fitting

13.) Connect red to red and black to black for power.  Trim the yellow wire flush or put a cap nut on it.

14.) For this next part, my boat was in the water so this was a little tougher but I got it finally.  The Echo transducer is held by two phillips head self tapping screws.  Remove these two screws taking extra care to not lose them.

15.) Assemble Lowrance transducer per the instructions.

16.) Using the 2 screws from #14 above attach the unit to the toon and make sure it is level.

17.) (If you're doing this on the water) Place a sandwich bag over the blue end of the cable and duct tape it closed so it stays dry.

18.) Tape the bag and cable to the Echo transducer cable

19.) Underneath the boat and half way up the transducer cable will be secured with a tie wrap. Cut this loose.

20.) Pull the Echo transducer cable back to this point and the Lowrance cable will come with it.

21.) Using the same mounting points and p-clips replace the Echo cable with the Lowrance cable

22.) Push the bagged end up through the access hole under the helm where everything else comes through (this is easier if you have a helper on the boat)

23.) Depending on the size of you boat you may need a Lowrance extension cable (not sure of the part but you can google it).

24.) Cut the tape, bag, and other cable loose.  Remove the Echo cable and do whatever you want with it.

25.) Install dash insert with Lowrance back into opening using the 4 nuts and washers from #2 above

26.) Connect blue power connector (it's keyed and must be locked in place)

27.) Connect blue transducer connector (again, it's keyed and must be locked in place).  Mine had 1" of length to spare so it was close

28.) Turn on ACC switch and then press power button on Lowrance.  Unit does not auto power like the Echo.  There may be a setting for this

29.) Go through the setup answering all questions.

30.) On a GCW2275 the water offset is 1'2" and I also checked the draft on my prop and it is 18" below water level.  You will need that first number for accurate depth and you should know the second one for your props protection

 

 

Tested the unit at slow speed and WOT and it worked perfectly.

 

Hope this helps.
 
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