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Registered 2001 SLK230
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Discussion Starter #1 (Edited by Moderator)
Add Always-Live USB to R170 SLK in glove box

Remember the days when they first put cell phones in cars (called car phones)? I do, and it was convenient because it meant your car had its own number, no matter who was driving it. Today, we can have a cell phone in the glove box, but it discharges. The answer is to have a live USB in the glove box with the phone on. As long as you drive regularly and have a good battery, the drain is not enough to kill the battery.

But where do you hook up the hot and cold wires? When I first asked, the good advice was that the SLK has so many sensors that hooking it up to anything other than the battery could introduce some gremlin of a problem. Good point. So here is how I wired the USB into the battery. It's mostly about access and not cutting holes where they could create new problems.

Note that this was done on a Made-in-Germany RHD 2001 SLK JDM, meaning made for the Japanese Domestic Market. It probably is similar or the same as US and UK, but I can't say for sure.

The most useful thing to know is that behind the passenger's footwell is a grommet with about 12 wire holes, and in my car there were only two in use (which is how I discovered the grommet in the first place)... a purple and grey that looked like they were some sort of aftermarket or option going from inside to somewhere near the headlights.

1. If it is a sunny day, put the top down. Why? Because after I removed the battery I discovered the doors had locked themselves, and of course I had tossed the key on the dashboard. If the top had been up, I might have been locked out. As it was, I reached in and opened the door. I think the doors locked when I disconnected the battery but I can't say for sure.

2. Remove the key and put it in your pocket. If you have an original MB Radio, make sure you have the radio code to reactivate it after you disconnect and reconnect the battery.

3. Disconnect the negative cable of the battery first

4. Then disconnect the positive cable of the battery and remove the battery (it is in the way)

5. Remove (in my case) the passenger side carpet (top half), and remove the protective cover beneath it.

6. With a Phillips screw driver remove the black plastic protector above the footwell. Two screws and then a sliding clip.

7. You will now see the grommet (use a flashlight)

8. Take a red wire for positive and press it into one of the empty slots in the grommet. Repeat in another slot with the negative using a black wire (colours are not necessary, but it is a good idea to signal to future owners that they are dealing with an unfused hot wire going straight to the battery).

It should look like this:

Underneath the battery box you will see the wires sticking out. They will look like this:

9. Run the red wire safely (not where the battery will touch them, wear away the insulation and cause a fire) to the electrical box where the heavy positive cable from the battery is connected as a junction box. It is a black plastic box with snaps to open it. Follow the (+) battery cable to find it.

10. Open it, and remove the 10mm bolt holding the (+) cable. With a proper Ring Eye terminal crimp the red wire, and then a few inches (cm) away, put in a proper in-line fuse on the red wire so any shorting does not burn up your car.

11. Slide the ring eye on the bolt and bolt the positive connection back together.

12. Use red zip ties to then hold the red wire so it does not move around and suffer abrasion. If you want to do a great job, then take a label maker and identify the red wire so some future mechanic knows what is going on. ("Hot wire to USB in glove box")

13. Locate the end of the negative battery cable, which is bolted with a 13mm bolt to the side of the engine compartment. Just follow the big cable and you will find it easily.

14. Take the black (-) wire you previously pressed through the grommet and install a larger ring terminal to the negative cable bolt and reinstall the bolt, again running the wire so it does not interfere, although damaging a negative wire is not as dangerous. Label it as well if you want to earn a merit badge.

The result should look like this:

15: Move to the interior of the car, and remove the black side panel that is exposed when you open the door. It is done with a large flat head screwdriver and it pops off. This will expose the back side of the glove box near the glove box piston.

16: This is the one place where you have to drill either two small holes or one large one.

17: I made two small holes separating (+) from (-). This is temporary. I am waiting for my mail order USB and when it arrives, I will drill a large hole so the USB is flush in the plastic.

Access looks like this:

18. Use common sense when running the wires from the grommet to the under-dash. Have a look at the most logical way to do it.

19. Inside the open glove box looks like this

20. Ensure the hot (+) wire is either properly wired in, or protected.

21. Put everything back together inside

22. Attach the negative cable to the battery

23. Attach the positive cable to the battery

24. Follow the instructions elsewhere on this forum to reset the car electronics.

Amazing that it takes 24 steps to do something as simple as run a hot and cold wire from the battery to the glove box, and for those who know what they are doing, all that they really need to know is that the German engineer anticipated that someone would want to add aftermarket wires from inside the car to the engine compartment, and installed an easy-to-access grommet with lots of extra empty slots.

The USB Converter arrived in the mail, and I thought it may be helpful to show how to install it. Seems I am not allowed to edit the original post so I'll have to add the final step as a reply.

[Moderator note:- Members with 15+ posts can edit for 10 days (not set by us), after that the mods will help for diy items like this - Myk]

  • Remove the side panel by the door
  • Connect the fused Hot (red) to the battery (see original posting) and the Ground (black)
  • Drill a hole in the glove box bigger than the USB
  • Slide it through
  • Install a rubber grommet in the hole to prevent friction on the wire
  • Neatly push the converter and wires back in and close it up

It works great. I have the phone on all the time so that the Aux on the radio plays bluetooth music by the press of a button rather than having to reach into the glovebox to turn it on. It also has the OSB-2 software on it hooked to the bluetooth OSB-2 unit. And it also works as a on-all-the-time car phone hooked through the radio so if the driver forgets to take a cell phone, they can be reached.


431 Posts
Why not do it in a simpler way?

just push the h.u. out, use a pair of Posi-lock, on h.u. wires?

you have there:
-always positive or -switched positive to choose, and -negative wires, and it will stay fused, as the fuses from stereo are lower values, in case of something wrong, it just blow, instead of that heavy duty fuses??

And with a semi-ridge wire, its easy to start from glove box and pass it to central dash (already stereo out...) and grab it there?

I've done this way, to put iPod on glove box.
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