I'm going to be installing a backup camera in my 2013 GLK250. My plan is to hook up the power (+) wire for the camera to the reverse light wire on the car. My question is, what's the easiest place to do that? Since the camera will be mounted to the tailgate, I'm hoping to find the wire on the tailgate itself somewhere, instead of running a wire all the way up the tailgate and then somehow down to where the light is. Thanks!

I found it a lot easier to connect to a wire near the head (control) unit in the dash, since that has to come out anyway. There's really no down side to not using the reverse light signal, since the camera draws a tiny amount of power, so it won't have any effect on anything as long as you choose a power source that turns off with the key.

I used the blue power antenna / amp sense wire coming out of my head unit, but it's on a 2011 with the slightly different NTG4.0 head unit. That might well be the same for the NTG4.5 unit in the 2013 though.

Here's the (inevitable) video that I made on the install process - I think it's pretty clear that it's easier to hook the power up to the radio harness somewhere (as long as the kit you have has a harness that carries a power wire back to the camera connection, which my ~$20 kit did).

Thanks for the (super fast) reply. Fortunately (or not, as the case may be) I'm going to be installing a camera that provides a wireless feed to the front of the car. There's no need to actually take anything apart on the panel as the wireless receiver will plug in to where the original Nav module used to be. I replaced that recently with an $88 replacement module that gave me Android Auto as well as a "dongle" to install the camera. For $90, I'm finding that module works very well!

Interesting option. I have a wireless backup camera on my RV, and haven't really liked it much because of the less than reliable link from the camera to the "receiver" (in this case, a device hanging on my rearview mirror), but it IS a "bit longer" than my GLK... (by about double). ;-)

I think the easiest way to connect is going to be to just open up the access to the rear light housings, and find the reverse light, and tap into the "non-ground" wire going to that socket. Should be pretty straight-forward, and certainly the current drain will be negligible.

[QUOTEI think the easiest way to connect is going to be to just open up the access to the rear light housings, and find the reverse light, and tap into the "non-ground" wire going to that socket. Should be pretty straight-forward, and certainly the current drain will be negligible.[/QUOTE]

Sounds like it. Although I'm going to try to find the correct wire in the conduit that leads from top of the hatch to the "C Pillar" that eventually goes to the light cluster in the rear fender. If anyone knows the color...:-)

Bumping my own post here for an update. I located the correct wire in the area of the reverse light in the left rear quarter panel and spliced a wire there. The only issue is that when I connect the camera to that wire, the camera stays on for a couple seconds, and then the image starts to degrade. As a troubleshooting step, I connected the camera to a different 12V source (the cigar lighter in the baggage bay) and it worked perfectly. I put an voltmeter to the reverse light and the voltage does vary a bit when I first put the car into reverse. Hmmm. I'm no EE, but I'm wondering if it might have something to do with the fact that the reverse bulb is LED? I'm tempted to simply connect the camera to a switched power source, but I'm unsure if having it constantly connected to power is a bad thing.
Any suggestions are welcome.

Do you have the option of connecting a supply line to the camera and a different sense line to the reverse light to make it come on?

As long as your head unit doesn't switch to rear view mode upon sense of video input, there's no down side to wiring the camera to a switched circuit. The current drain is negligible.

I'm pretty sure that the NTG4.5 head unit doesn't rely on video sensing, but switches based on a reverse mode, just like my NTG4.0 head unit.

Not 100% sure I understand your question.

The NTG4.0 head unit gets the reverse gear signal from somewhere other than the reverse light circuit. I assume the NTG4.5 does as well. When I installed a new NTG4.0 head unit that had been programmed for reverse camera, the rear view screen came on even though there was no camera.

If you're familiar with adding an audio power amp, it will have a power lead that goes to a power source, and a sense line that tells the amp to turn on when the radio is on. Same thing with a powered antenna.

Ok, I see.
I ended up powering the camera to the switched cigar lighter in the cargo area. That seems to be working

You could use a relay as well. Use the reverse light signal as the relay trigger and the switched voltage as the power.

No need for a relay - a reverse camera draws a tiny fraction of an amp, so no need to isolate it from the feed. I powered my camera (NTG4.0 install in a 2011 GLK) from the antenna / power amp sense wire coming from the head unit. So the camera's on any time the ignition is, but that won't ever matter - not enough current drain to make any difference.

Since the OP is using a wireless camera, powering it continuously while the car is running will greatly reduce the lifespan of the camera as it is transmitting all the time. By installing a relay it will just transmit while the car is in reverse.

Nit picking, I know, but, what happens if you turn the radio off?

With a wireless camera (and more importantly, receiver) I don't think you can just have the camera on all the time, since (at least on the wireless rigs I've seen) that will default to being in rearview mode all the time. If there's a wireless camera hooked to the stock NTG4.0 or 4.5 head unit, it should be OK. I doubt you'll wear out the transmitter, even leaving it on any time the car is powered up.

If the head unit is powered on, the antenna / power amp sense wire is hot. At least I've never seen my rearview camera not come on no matter what mode the head unit is in - other than entirely off, in which case the screen is off anyway...

I'm still waiting for the wireless transmitter and receiver to arrive, but in my testing using a wire, yes the camera is on whenever the car is running, but the OG head unit doesn't display the camera screen unless the car is in reverse. Of note, I'm not using the Becker NAV module in this vehicle, but rather a plug-in replacement that I bought on the Internet. Mainly bought because a) the Becker module went "tango uniform," and b) I wanted Android Auto. The unit includes a dongle for, among, other things, a dongle to plug in a video camera. That's what inspired me to but a camera in the first place. If for some reason the wireless components don't work, I'll just take an extra couple of hours of cursing and run the wire permanently and try the wireless thingy on my '76 VW Bus. :-) For less than $100, I'm quite pleased with the setup.