Author Topic: HELP! - Wiring connecting VHF to 797 for DSC  (Read 9371 times)

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Offline akgoff4

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HELP! - Wiring connecting VHF to 797 for DSC
« on: May 14, 2011, 03:18:19 PM »
HELP :-[

I am trying to hook up my 797c2si to my Cobra MRF-55 VHF marine radio so that the 797 transmits GPS location to my marine radio, so if I ever have to push the DSC distress button, the Coast Guard receives my GPS coordinates automatically.  I have the GPS cable from Cobra.  I have NMEA output set to "on."

I have attached a crude wiring diagram of the way things look under the console. I am not real confident that the marine dealer that hooked up my HB did it exactly right, although it seems to work fine.  (He's out of business now.) 
On my drawing, the white wire from the "pigtail" is in shown in gray.  The "W" is my Weathersense.  The TCAP is the HB Unit. ( T for Transducer.  C for Com. A for Access  (unused). P for Power. )  The wires coming from the

 I am also attaching a diagram that was posted elsewhere on this site.  Looking at this diagram leads me to believe that my unit is currently hooked up wrong.

I believe that I am supposed to hook the red wire cobra wire to the white NMEA output wire.  But what do I do with the black ground wire from the Cobra? 

Is the red wire that comes out of the NMEA cable supposed to be wired into fuse box? In the second diagram I attached, leads me to believe it was supposed to be capped or terminated.

 What about the ground wire that comes from NMEA?  Leave it where it is or disconnect it and hook it to the black wire from the cobra unit?  (which seems to make sense to me.)

Another HB document that was sent to me by HB says use AS-HHGPS which is the Handheld GPS cable. I ordered that cable.  However the instructions they sent me is for a 797 with an internal GPS. 


Offline Humminbird_Greg

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Re: HELP! - Wiring connecting VHF to 797 for DSC
« Reply #1 on: May 16, 2011, 02:40:26 PM »
That second posted document is mine and is the correct way to wire your 797c2 Si unit to your DSC radio.  Return the AS-HHGPS cable as you do not need it.

I donít know what the Red and Black wires for your Cobra DSC VHF radio are but what you stated sounds correct or at least it would be for a Cobra MRF55 as that is what it shows in the instructions for that model.  I suspect that the other model Cobra radios are the same but check your operations manual to be sure.  So if that is true:

Connect the Humminbird NMEA White wire to the Red wire from the Cobra radio.
Connect the Humminbird and Cobra Black wires together.

Hopefully this will work but it may not as by your drawing it looks like your system may have placed +12 volts from your battery on the NMEA communications bus and I donít know what this may do to the internal components of the unit or the GPS Receiver Ė but Iím keeping my fingers crossed for you (which incidentally hasnít slowed my typing down any).

The Red wire should not be connected to anything and needs to be terminated so that it doesnít.

Greg Walters at Humminbird

Offline akgoff4

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Re: HELP! - Wiring connecting VHF to 797 for DSC
« Reply #2 on: May 18, 2011, 06:11:41 PM »
I suspected what you said was the case.  However, when I clipped the red wire and black wire from the pigtail and taped them up .  Before hooking up the VHF, I tried to turn the unit back on but nothing happened - it was getting no power at all.  Hmmmmmm.  Do you have a basic wiring schematic for the 797 hook up? Don't you  just take the red power wire from the unit and put it in fuse box and ground the black wire?  I guess I am going to have to rewire the unit from scratch. 

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