The E92 M3 without sunroof does not have a proper grounding screw above the map lights. Therefore, tapping into a hot lead above the map lights as some DIYs suggest will not work unless you have a sunroof and a ground. Furthermore, any electronic malfunction, from a dealership perspective, can actually be blamed on tapping into wires. So, here is the other method.
I am expanding on E92Vancouver's DIY here: http://www.e90post.com/forums/showthread.php?t=111583
using the Safe-N-Sound radar hardwire kit.
I am adding more detail, and this method will NOT remove trim.
Here are the tools you will need.
- A directwire kit of some type. This one is the Safe-N-Sound kit (see ebay; very affordable)
- Add-A-Circuit mini (about $15 at most automotive stores)
- 3 amp fuse provided in the Add-A-Circuit kit
- A larger ground loop
- Grips (small set for accuracy, big clamps for smashing the connectors together)
- 4mm hex head screwdriver
- Zip ties
Step 1: Run wires
Place the detector where you want it and approximate the amount of wire you will need. This will come in handy when you decide where to bunch up the extra or if you even have enough in the first place.
This DIY suggest you run along the headliner towards the passenger A pillar. Then, run around that A-pillar at the joint until you hit the door trim (where it meets the A-pillar). Then, tuck all the way down the door rubber until you hit the entrance to the glovebox.
Step 2: Access fuse panel, and thread into the glovebox
Access the fuse panel by opening the glove box and turning the two retaining bolts on either side of the back of the glovebox 90* each so they are vertical. The panel should fall forward exposing the fuse box.
Tuck into the glovebox where you find an opening near the bottom. You can see it in this photo, taken from the floor looking up.
Step 3: Wire your add-a-circuit and ground loop
The kit from safe-n-sound does not come with a large enough ground loop to fit the screw we will use. Pull it off and crimp a larger one on. This ground wire will be attached to the large hex head screw found to the left of the fuses. Before you screw it on, wire your hot lead!
You will need to replace the connector provided by safe-n-sound on the hot +12v lead to your add-a-circuit. In my case, I had a t-tap kit on there designed to be the female end of a wire tap. Pull it off, and crimp on the add-a-circuit. The Add-a-circuit has two slots for fuses. The bottom one/slot A/closest to the fuse plug is the "original" fuse you will be replacing with. Slot B (top one) will be used for the detector.
Step 4: Plug into fuse #8 and screw in the ground
Pull out the 20A fuse and plug it into slot A of the add-a-circuit. Plug the 3A fuse provided with the kit into slot B of the add-a-circuit. Plug the add-a-circuit into fuse position 8. Fuse #8 corresponds to the cigarette lighter aka accessory plug. So it makes sense to use this and will turn off with the vehicle.
Pull the screw off and place your ground loop between the chassis and the screw head.
Step 5: Conceal wiring
Tuck the wire all along the headliner until you reach the a pillar. Get out a trim kit tool and push into the A-pillar until you reach the trim joint about an inch down from the roof. Follow the trim joint around until you reach the door rubber. Tuck under the door rubber all the way down until you reach your entry point to the glovebox. This was incredibly annoying. I actually didn't even get the wire completely concealed between the glovebox and door rubber near the bottom. Thankfully, it isn't noticeable. Recommend a good amount of beer for this step.
Clean up in the fusebox by using zipties to secure your wires to the main harness. Close up the fusebox by aligning the tabs on the fuse panel vertically and turning them horizontally 90*