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Shortening a GTM-25 cable for hardwiring

Hello everyone!

This is my first post, it's nice to be a participant in these forums.

I still use a Nuvi 1450LMT with a GTM-25 traffic cable. My project is to cut off the bulky cigarette lighter plug to hardwire everything using an add-a-fuse fuse tap and a step-down voltage converter.

1) I am aware that a voltage conversion process takes place in the plug (12V to 5V); no problem as I have a step-down converter;
2) I am aware there is a fuse in the plug tip.

My question is this : how many (and which) wires go up the cable, past the plug? Only a black (neg) and a red (pos)?

I really wish to hardwire it all, but before I cut wires I would appreciate knowing what goes up the wires after the plug, but before the traffic receiver.

I can't find a lot of information on the web, I admit this GPS receiver it kinda dated now.

If you can provide some insight, THANK YOU very much!


  • Boyd 2002 Points
    I think the traffic receiver circuitry is actually inside the plug on that model, isn't it? So if you want that to work, wouldn't you have to "dissect" the plug and retain that circuitry? Seems like a much easier solution would be to wire a female cigarette lighter outlet to your fuse and bury it in an inconspicous place. Then you could just plug the whole thing into the outlet. I know some people do this by purchasing a cigarette light extension cable, cutting off the male plug and directly wiring that.

    Also, the traffic receiver uses the wire as an antenna, and was intended to be exposed to receive a good signal.
  • The traffic circuitry seems to be in a small plastic rectangle housing (the size of a Bic lighter), about 8 inches behind the mini-USB plug that goes into the 1450LMT. I also think the cable is used as an antenna.

    Oh well :(

    The setup you are suggesting is what I use right now, it works fine... I must have some obsessive-compulsive disorder, as I really wanted to make things neater since the free space around the fuse box is scarce, the remote start module is huge and in the way...

    Thanks for your reply, Boyd!
  • Kevin_hutch 115 Points
    The USB cables are a can of worms, compounded by the traffic receiver, not impossible but fraught with danger. I would be finding a place to locate the cig socket and plug even if you need to extend the cable from the fuse to the socket, then if/when you update your GPS to one that needs a micro USB you will not have to start again.
  • AndreyT 105 Points
    edited April 2018
    Judging by the picture of the cable, its internal structure is similar to the traffic cable that came with Nuvi 3490. The cable between the traffic receiver and the cigarette plug has two asymmetrically sized parallel sections, separated by a lengthwise groove. The wider part carries the power through a coaxial wire (both + and -). The narrower one contains the traffic antenna, which is just a length of wire. The antenna is connected at the traffic receiver end, runs the entire length of the cable all the way to the cig adapter, but doesn't really enter the adapter. It does not connect to anything inside the cig adapter. So, you can safely cut the cable at the cig adapter. You can also cut the wider (power) side of the cable to make it shorter. But you should not shorten the narrower side, since it is your antenna. A good idea would be to separate the cable by cutting through the groove lengthwise and the routing the power and the antenna independently. The power part can be shortened as much as you want.
  • Hello AndreyT!

    Thanks for your reply. After I read your post, I decided to just go with it and cut the cable! In my case, the narrower side was indeed the traffic antenna (and not connected to the circuit board as you said).

    The wider side had two "grooves" in it, but there was only one cable with a shielding over it... so there was no cable in one of the two grooves, it was empty! The voltage is inside the cable and the shielding acts as a negative.

    Everything works! I tried my setup indoors with the voltage stepdown module and everything was working flawlessly, even the traffic receiver. I'm glad I am going to get rid of the bulky cigarette lighter plug and socket it was plugged into!

    Thanks a lot and have a great day!
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