Finding correct wires for mirror tap

[arktis 58]

I'm trying to find a 12v and GND wire in my rear-vision mirror to hardwire a radar detector, but I can't seem to get the right wire. I've tried fiddling around with a multimeter, but I'm not certain how to find 12V and GND.

I've loaded up the diagram in ISTA and I have no idea what I'm looking at. I was expecting it to give me a pin-out with the voltages of each pin listed.

Is there somewhere else I should be looking?
Is GND always brown?
Has anyone done something similar in E60/E63/E64 and knows what wires to use?
Might I need to strip the wire for my taps to contact?

No laughing please, I'm a total dipshit when it comes to electrical (and most other automotive topics, really 😆)

Here's a pic of the product I'm using:

[kwhelan 241]

https://www.bimmerfest.com/threads/schematics-for-rear-view-mirrow.1459181/

no stripping for taps

the pinouts are in there but your on the wrong page there, its not an easy thing to browse but its in there somewhere, if you find the module number of the plug you can search for it

brown is definitely common for earth but not guaranteed ,put your mutlimeter in buzzer mode for loop testing i(t will make a noise when you touch leads together) and you can check the brown wire to a metal part of body or car, if ir makes a noise its connected,

make sure you test between two metal parts of the car first to check your actually touching metal not paint, confirm you are touching a good earth

for power set multimeter  to dc volts probably something like 40v on the tool and look for a 12 v reading when the other lead is connected to the car body metal, test with key on and off , be aware alot of circuits don't go to sleep immediately when the key is off so make sure car has powered down and leave window open as opening the door will wake up some circuits

Edited December 30, 2023 by kwhelan

[arktis 58]

Thanks Kevin. I'm reading through this thread now.

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 if you find the module number of the plug you can search for it

Searching isn't giving me much. I've searched for X18246, and 616035. Nothing gives me a pinout.

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no stripping for taps

Cheers for confirming this.

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put your mutlimeter in buzzer mode for loop testing

I don't know if my multimeter has buzzer mode, I've got this cheapo one here: Medalist | Digital Multimeter 150x70mm Orange | Mitre10

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be aware alot of circuits don't go to sleep immediately when the key is off so make sure car has powered down and leave window open as opening the door will wake up some circuits

My understanding is that the accessory circuits stay on for 8 minutes after ignition off.

 

[arktis 58]

I didn't have any luck with the multimeter so far. I couldn't find anywhere to ground. I'm scared to use the cigarette lighter again because last time the probe slipped and I needed a new fuse 😂

I found this image, which is helping to make sense of what I'm seeing on ISTA:

 

Seem right? Gonna go fiddle and see if this does the trick.

[arktis 58]

The signal codes were gleaned from the forum post @kwhelan linked.

[Eagle 1662]

Looks ok . Never seen a BMW where brown wasn't ground. You'd need to insert a pin etc first into the back on the mirror connector to find 12V because normal multimeter leads are too big. 

You can always put a terminal on the ground wire and use an existing screw\bolt around the area to ground it to the roof\body, i think that was i did with mine to avoid to avoid using another tap, 

[arktis 58]

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You'd need to insert a pin etc first into the back

Yeah, noticed this. I reckon some test lead adapters would be quite handy. I've used staples before, and they don't really stay in place.

No luck with green/yellow, somehow... Tried in accessory mode, ignition on, the lot. FWIW, I've verified that the detector powers up when connected straight into a 12v battery.

Does it matter which side of the plug I use? I'm tapping into the back of the car-side of the plug, as opposed to the back of the connector on the mirror-side. Mirror-side is really difficult to access.

[Eagle 1662]

Ive never used those style leads, only wire or fuse tap, they dont look secure to me but if you sure the pins are making good contact then you probably need to probe the wires and verify 12V with the meter.  Is that wiring diagram accurate?

If you do have power on the green\yellow then its probably not making a good ground connection so id go for the above or wire tap. 

Not sure what are you saying about the plug. You can only really tap into the back of the harness connector (carside) with what you are using

[arktis 58]

The pin broke off the positive, so I'm a bit stuck now :)))

I'll fix it, and try grounding it to a bolt with an eyelet terminal. I think I need to buy a kids' electrical starter kit so I can learn how to process electricity in my mind.

[Eagle 1662]

If the wiring colours match up with the diagram then its probably accurate. If you insert a pin, paper clip etc into the back of the green\yellow connector so it touching the metal (the one that connects directly to the mirror, under plastic trim?) You should read +12V with the multimeter set on 20 position with the red lead on the pin yellow\green wire and black lead grounded to bare metal (screw\bolt on body\roof)

I think its a connection issue with your pins but i you'd need to post photos of what you are talking about regarding the connectors above as im not familiar with E63 wiring or what you trying to do exactly.

Id just install one of these - https://www.jaycar.co.nz/double-standard-blade-fuse-socket-wire-tap/p/SF5115?pos=3&queryId=2eea1039fdd6f7f968f4337ac7e42a5f&sort=relevance&searchText=Fuse Socket Wire Tap

Running a wire from fuse box, up pillar trim isnt that hard and you shouldnt have to take off much besides pillar trim, maybe the glove box then at least you got a perfect connection with a separate circuit

These work well but never seen them in NZ  

 

[kwhelan 241]

think your making hard work of your meter to be honest,

make sure you get 12v across your battery to confirm you even have the meter on the right setting first, probably says 40v or something similar, needs to be over 12v for sure

all meters have a loop test circuit, you won't do any damage if you change the dial, hold leads together and fiddle until you find it as I can't quite see from pic

make sure you understand the pin numbering is being reversed because your looking at the back of the plug,

playing with something like a staple in the back of a plug is asking for fuse blows, just too small and fiddly

try stripping a piece of wire or maybe a paperclip wrap it around the red probe 3 or 4 times tight with a 20mm extension so its tight/firm on the red probe then you have a  smaller point to insert into plug

and use black probe to earth somewhere near on the roof so the two leads arn't side by side and can touch and blow the fuse by mistake

confirm your earth lead is  actually earthed by checking for a loop between two metal points on car, door hinges are usually good points for earth

one of those wires in the mirror plug has 12 volts so if you can't find it your not connecting correctly

lastly I would have thought if you have used lighter circuit before you already know those wires so no lead required

BTW pack of 100 assorted fuses is like $5 ON AliExpress , always have a pack handy

Edited January 1 by kwhelan

[arktis 58]

The meter was looking good, had some 12v reads that made me feel like I was on the right track.

I'll go over to Jaycar when I can and grab a few bits to have another go at this. I know it shouldn't be this complicated.

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make sure you understand the pin numbering is being reversed because your looking at the back of the plug,

Thankfully the plug is asymmetrical, and included on diagrams, so it's quite easy to know you're heading in the right direction.

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Running a wire from fuse box, up pillar trim isnt that hard and you shouldnt have to take off much besides pillar trim, maybe the glove box then at least you got a perfect connection with a separate circuit

In a way this seems way easier, but I hate how much extra wire it takes to go this route, when I should be able to get the mirror taps working. Maybe some smaller taps that I can get a bit further into the plug would help.

Thanks for your help guys. I'll get to the bottom of this.

[aja540i 1906]

Probably easier to find a constant 12v source in the interior light and not far to run a piece of wire if you need to?

[arktis 58]

I got a couple of bits from Jaycar and I’ll have another run at this in the weekend.