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Jul 14

How To Hardwire a Radar Detector

Radar detectors need to be plugged in for power and generally ship with a cigarette lighter plug to make it easy to power your detector. However, it looks kinda ugly to have a long cable dangling down your windshield and dash and it can get in the way of using your stereo. It also makes it obvious to others while driving or parked that you have a detector so many people take their setups down when parking and put everything back together every time they get back in their car.

A good alternative is to hardwire your detector by creating a permanent power plug for it.

Hardwired DFR7

Rather than taking up your cig. lighter outlet, you power your detector from your car’s fuse box and run a power cable hidden along the trim of your vehicle to create a much cleaner and professional looking installation. It allows you to mount your detector high up near your headliner for better radar detection, your detector can be more stealthy behind your tint strip without the cable dangling down so it’s less visible to police or potential thieves, you can leave it in your car with less chance of someone else seeing it, etc. There’s lots of great benefits to doing this and it’s the preferred method to power your radar detector.

You can hire a professional to do this for you. Most any car radio installer can do this and it doesn’t take a lot of time or money, or you can do it yourself. In this tutorial I’ll show you how to do it yourself.

What You’ll Need

  • Hardwire cable
  • Add-a-circuit fuse tap kit
  • T-tap (optional)

Hardwire Cable

Direct Wire Cable

So the power cable that you’re going to need is called a hardwire cable or direct wire cable. It’s basically a long straight cable that connects to a power source on one end and plugs into your radar detector on the other end.

There’s a variety of different types. Your traditional hardwire cable is just a simple power cable. Some fancier ones add in an additional remote mute button and alert LED, some add bluetooth so you can pair your detector to your phone, and so on, but the principles are the same.

There also specialized ones like short cables that plug into your auto-dimming rearview mirror or your OBD-II port to provide you with alternate locations to power your detector from.

If you want to see all the different options, see this article on Radar Detector Hardwire Cable Options. For now to keep things simple, we’re going to talk about just your standard simple power cable that runs down to your fuse box.

Add-a-circuit Fuse Tap

Now to actually get power for your radar detector, you’re going to want to tap into your fuse box.

fuse box

(Image credit: napaonline.com)

The fuse box is located in different places in different cars, but inside you’ll see lots of little fuses for different parts of your car: AC, stereo, power seats, airbags, etc. We’re going to add your radar detector so that it’s also tapping into the fuse box like all your other electronics. (You can do the same thing with your dashcam, laser jammers, phone charger cables, etc.)

To actually tap into the fuse box, you’ll need something called an add-a-circuit.

Add a circuit

An add-a-circuit lets you add new electronics to your existing fuse box. Now different cars and manufacturers use different size fuses so you’ll need to get the one that’s the right size for your car. You can either Google it, check your car manual, or just pull a fuse out of your car and compare it to the guide below.

Fuses

Once you figure out which fuse size you need for your car, you’ll want to pick up an add-a-circuit kit for the the size fuse you need. Here’s where you can get the kits for the most popular fuse sizes:

Micro2 add-a-circuit kit

Low-profile mini add-a-circuit kit

Mini add-a-circuit kit

ATO add-a-circuit kit

(A kit usually includes both the add-a-circuit cable plus some extra fuses you’ll need for the new devices you’re adding.)

Plug In the Add-A-Circuit

To plug in the add-a-circuit, you’re going to want to find a fuse in your fuse box that turns on and off with your car’s ignition. Generally some circuits are always powered while others are tied to your ignition. You’ll want to use something that turns off when you turn off your car so that your radar detector doesn’t drain and kill your car battery when you’re parked. Then when you start your car up next, your detector turns back on. Now you’ll have to poke around because this is different with every car. To find out what each fuse goes to, you can either check your car’s manual or the diagram that’s often located on the cover to the fuse panel. It’ll look something like this:

Fuse box guide

Note: Some cars don’t have any fuses that turn on and off with the car and every single fuse always has power no matter what. If this is the case for you, you may need to turn your detector on/off manually every time. Some GPS-based detectors have an option to automatically turn off when they sense that you haven’t been moving for a long period of time, aka when you’re parked.

Once you’ve found a fuse slot you want to use, you’ll want to pull out the existing fuse. You can use a specialized fuse puller to do this, but if you have a set of thin pliers on hand already, that can often do the job as well.

Once you get the fuse pulled, you’re going to want to put that fuse in your add-a-circuit which has slots for two fuses. The bottom one (farther from the red wire) is the one for the original fuse you just pulled. The top one (in line with the red wire) is for the new accessories (radar detector, etc.) you’ll be adding.

Add-a-circuit fuses

Now the add-a-circuit kits I linked you to above all include some extra fuses specifically for this second slot. You’ll want to add up the maximum power usage used by all your devices and pick a fuse that’s a little larger than all of them combined. For example, if you’re using a RD that uses 500 mA or 1A total, a 2A fuse is good. If you’ll be putting multiple devices on that add-a-circuit, you may want to use a 3A or 5A fuse.

Here’s the add-a-circuit tapped into my car’s fuse box.

add-a-circuit in my fuse box

Connecting To The Add-A-Circuit

Once you have your add-a-circuit installed in your fuse box, you’ll need to connect your hardwire cable to it. There’s two main ways to do this.

The first is to use the blue connector on the end of the add-a-circuit. You can strip the end of the power wire of your hardwire cable if it doesn’t come stripped already, insert it into the blue connector, and use a crimper (not pliers!) to crimp down on the blue connector and make a good solid connection. Personally I don’t generally use this option because it only works for one device and it’s not removable if you want to swap hardware later, but it definitely does the job and is a pretty simple solution.

Add-a-circuit crimped

(Image credit: mazdaspeedforums.org)

Your other option is to use a T-tap which bites directly into the red wire itself, making contact with the electrical wire inside it.

T-tap on add-a-circuit

(Image credit: hkwonger.blogspot.com)

You see the metal part inside the blue T-tap? When you close the T-tap, it bites down on the red add-a-circuit cable, cutting through the red insulation, and making contact with the wire inside. It helps to have a set of pliers to squeeze down on the T-tap so that it cuts through the insulation and clicks closed.

Once it’s locked down, you can slide on the matching connector from the hardwire cable (assuming it has one) and you’ve got a power connection for your radar detector.

T-tap attached to add-a-circuit

(Image credit: hkwonger.blogspot.com)

Now the add-a-circuit kits I linked you to earlier all include the T-tap and matching connector. The hardwire cable you chose may or may not come with the connector that slides onto the T-tap. If not, you can either buy them separately or just use the crimping trick I showed earlier onto the end of the blue connector. If you need some T-taps and/or connectors, you can get some here. (I usually like to buy a set of them so I can add multiple devices like dashcams, laser jammers, phone chargers, etc. to the add-a-circuit, plus you usually can’t buy just one anyways.)

Connecting Your Ground Wire

Your hardwire cable is made up of two wires: power and ground. Power you get from your add-a-circuit. Ground you’ll need to connect to elsewhere. You can either find a ground wire from some of your existing electronics and tap into it, or you can connect your ground wire to a metal part of your car’s chassis.

If you have a ground wire you can tap into from something else, and there’s often some around the fuse box anyways, that’s the easiest way to go.

If not, look for a part of your car’s chassis or frame, not just some random piece of metal floating around anywhere, and securely affix your ground wire to the chassis and now you’ll have a solid ground for your detector.

Running the Wires

Once you’ve got the hardwire cable connected to your add-a-circuit and ground, it’s a simple matter of plugging everything in and running the wires. You’ll generally want to run the wires from your fuse box, up your A-pillar, across your headliner, and into your radar detector. Often times you can simply tuck the wires behind the body panels, but sometimes you may have to remove panels to get the cleanest install. (Note: Make sure your wire doesn’t run over top of the airbag in your A-pillar!)

Here’s a look at where my hardwire cable is run along my car.

Radar Detector hardwire cable run

That’s it!

Now you’ve got a professional looking clean install, your cigarette lighter outlet is free for other devices, you can mount your detector in the best possible location for radar detecting performance (up high), and you no longer have to deal with ugly cables hanging down your dash and getting in the way.

Once you get your install completed, feel free to share it with the community in the Show Off Your Install section on RDF.

Enjoy your beautiful new install! 😀

Video Tutorial

Bonus: If you’d like to watch a video walkthrough of the installation process, here’s a video tutorial with me hardwiring both a radar detector and a dashcam into a vehicle.

13 comments

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  1. Alvin

    Hi Vortex,

    Just wondering, if I have multiple devices I’d like to hardwire, for instance a dashcam and my radar detector, can these both be T-tap’d to a single add-a-circuit?

    Many Thanks!

    – apex

    1. Vortex

      You bet! That’s exactly what I do. 😉

  2. Greg

    How do I determine if my fuse box is “hot all the time”? I did essentially what you did: direct wire cord and add a circuit and used the radio fuse:

    https://images-na.ssl-images-amazon.com/images/I/71yLEAwleWL._SX522_.jpg
    https://images-na.ssl-images-amazon.com/images/I/51f6Locn%2BAL._AC_UL160_SR160,160_.jpg

    However, my detector doesn’t turn on/off with the car. Instead, I have to manually turn the detector on/off.

    Also, several reviews on Amazon (for the direct wire cord) mentioned something about “reverse polarity” – would that have an effect on why it’s “always hot”…?

    1. Vortex

      So there’s a bunch of fuses and they’re all for different things. Some will be for things that should always have power (like your dome lights) while others will be for things that should only work when your car is turned on (like your stereo). It varies from car to car so you may wanna try a different slot in your fuse box.

  3. Greg

    I used a multimeter and verified that every fuse slot has 12v (hot all the time), even when the car is turned off. In this case, what can I do to direct wire the detector and have it come on/off when the key/engine…?

    1. Vortex

      Yeah this is the case with some vehicles, unfortunately. Some GPS-based detectors come with the ability to shut themselves off automatically when they notice you’ve been stationary (parked) for an extended period of time, this way they don’t drain your car battery. That’s one solution that’d work.

  4. Rick

    My radar hardwire is interfereing with my tire pressure sensors. Its not allowing the valves to communicate with the computer. Any fix for this so the tire pressure sensor fault light doesnt stay on?

    1. Vortex

      Weird, I’ve never heard of this happening. Maybe try tapping into a different power source if you’re seeing conflicts in where your RD is drawing power from?

  5. Don

    So, I took your advice after viewing several of your videos and purchased the Uniden DFR7. I was hoping to hard wire it to my fuse panel but see that it has a RJ45 connector on the power cord. I haven’t been able to find any info on hard wiring this type of power cord to a fuse panel. Can you help?

    1. Vortex

      Sorry I’m not sure what you’re asking. This article you’re commenting on is designed to show you exactly how to do that. You use a hardwire cable, one end goes into your RD and the other end goes into your fuse box. What’s your question, exactly?

      1. Donald Kalina

        The power cord connector to the radar detector isn’t a USB or MICRO, it is a plastic RJ45. I haven’t seen any hard wire kits with this type of connector.

        1. Vortex

          RJ45 is the standard power connector for radar detectors and most hardwire kits are designed for it. Here’s one: http://bit.ly/28TJdLb and here’s another: http://amzn.to/2q7AeeI

          1. Donald Kalina

            Thanks, since my last email I found a hard wire kit for the Uniden on Amazon. Appreciate your help.

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