Opinions needed: Repurposing this wiring for my CEL

[2mAn]

Ive had this wiring sitting loose and dont really know for sure what it is for. Most recent idea is that its for a brake lining sensor, since its in/near the driverside wheel well.




My car doesnt have ABS, it didnt have an OBC so the brake lining sensor is most likely the correct original use of this wiring. However, I dont have a brake lining warning light ON in my cluster, but that could be just because the bulb has been removed (havent verified this).

Anyways, my car hasnt had the M10 that it came with since the 90s, if that. It currently has a M52 swapped in, and I dont have a CEL either. Im wondering if I can use this wiring and connect it to the X20 and save myself the trouble of routing and tucking wiring, especially since this wiring already seems to serve a similar purpose.

thoughts? opinions?

[TobyB]

I did a lot of that when I built my car- grab the ETK and compare colors.

Then verify with an ohmmeter.

Then have at it!

I get diff temps through the rear lining sensor wires and so forth- works great, no rewiring.

t

[2mAn]

bumping this back. I recently replaced the gears in the odometer, so I was checking out the bulb situation and sure enough the brake lining bulb was removed After installing a bulb the light was illuminated. Now I have to figure out how to use the wiring to connect it to the 413 ecu's CEL functioning... I hate wiring...

It should be simple, but Im a dumbass with this stuff. so pardon the stupid questions.

#1 If I cut the Brake Lining connector and connect the two wires (Green/Yellow & Black ?), that should turn the light off. correct?

From what Ive found is that Pin 8 on the X20, a grey wire, is the only wire for the check engine light, so...
#2 Would I need to connect that grey wire to the green/yellow wire or the black one?

Obviously I can cut all the wires and start playing around but I really dont want to make a mess until I sort of have an idea of what to do.

[smooth]

If you connect the two brake lining wires it'll turn the light off. You don't need to cut them, however, you can just put a wire inside the connector and tape it.

[2mAn]

That only helps with shutting the light off, not the more important part of using the wiring that already goes to the cluster to be a CEL instead of a brake lining light

[smooth]

What are you asking help with? I answered your question #1 as you wrote it


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[2mAn]

The CEL is routed from the 413 ECU to the cluster from a gray wire (pin 8 om the X20 plug).

The brake lining light turns off when the circuit is completed when the two wires are connected.

Which wire would I need to connect the grey wire to, in order to use the brake lining light as a CEL. This is confusing for me because the brake lining light is essentially using both wires.

http://wedophones.com/Manuals/BMW/1984%20BMW%20318i%20Electrical%20Troubleshooting%20Manual.pdf

Page 30 has the brake lining diagram

[vpilarrt]

I think I understand, since your car (an 84 318i) doesn't have a check engine light you want to use the brake lining light as your CEL. Right? The problem is the brake lining sensor is essentially an open or closed switch and the CEL signal from the ECU is more than likely a voltage. If you want to do this you'll have to run your gray wire into the instrument panel and connect it to the non-grounded side of the brake lining light and cut the circuit board trace that goes to that side of the light.

[2mAn]

I think I understand, since your car (an 84 318i) doesn't have a check engine light you want to use the brake lining light as your CEL. Right?

Correct!

The problem is the brake lining sensor is essentially an open or closed switch and the CEL signal from the ECU is more than likely a voltage.

That is what I have been trying to say, but Im a wiring idiot and cant properly explain...

If you want to do this you'll have to run your gray wire into the instrument panel and connect it to the non-grounded side of the brake lining light and cut the circuit board trace that goes to that side of the light.

I was with you and then you lost me haha...

I feel like the green/yellow wire would NOT be the grounded side.

[vpilarrt]

Neither of the wires coming from the sensor are grounded. You can't do this without modifying the instrument cluster.

[2mAn]

Neither of the wires coming from the sensor are grounded. You can't do this without modifying the instrument cluster.

if I connect the gray wire to the green/yellow wire and ground the other, would that work (edit: or connect it to a 12v source???) ?

...you seem pretty knowledgeable with this stuff. what do you recommend doing?

I HAVE to have a CEL to make my car street legal in CA

edit: found this here

Its pin 8 (gray wire) on the m50 x20. Find a 12 volt switched power source, wire it to a light either in the cluster, or where ever you want it. wire the negative side of the light to pin 8 of the x20. your done.

using his explanation it still sounds like I can use the Brake Lining wiring. pin8 on the x20 to one of the wires (green/yellow since i keep wanting to do it that way), then the second wire would need to go to a 12v source?

[vpilarrt]

OK, so (according to the info in your link) the ECU supplies the ground to turn on the CEL. Unfortunately the ground for the brake lining light is also the ground for the gauges in the instrument panel. An easier solution would be to use the parking brake light. If that's OK with you I can write some instructions on how to use that one.

[DaveSmed]

You could just add a pull up resistor to the cel circuit, and use the brake lining light still.

[2mAn]

oh man resisters ... as if I wasnt already scared enough

[Jaxx_]

Neither of the wires coming from the sensor are grounded. You can't do this without modifying the instrument cluster.

I agree.

Its pin 8 (gray wire) on them50 x20. Find a 12 volt switched power source, wire it to a light either in the cluster, or where ever you want it. wire the negative side of the light to pin 8 of the x20.

using his explanation it still sounds like I can use the Brake Lining wiring. pin8 on the x20 to one of the wires (green/yellow since i keep wanting to do it that way), then the second wire would need to go to a 12v source?

Not quite. the brake lining wiring doesn't go directly to the bulb, this is why you have to modify the cluster.


Basically, you have a light the "ground side" of the light is connected to your x20 pin 8. The other side is switched with 12V. You can find this somewhere on the cluster, and solder a wire to your selected bulb(check engine light I suppose).

Honestly I think you will have an easier time just running 1 wire to the cluster than dealing with having to modify MORE wiring on the cluster in order to use the brake lining sensor.

Here's what you need to do: Find a switched 12V source--I think just start/run--in the cluster(using a multimeter this should be pretty easy). [edit:Now that I think about it, many of the lights will probably already be in this configuration... you can test it.] Solder a wire from that point to the metal contact of the bulb holder/hole you would like to use. Cut any other connections to that bulb holder so you don't fry anything. Then wire your X20 Pin 8 to the other side of the bulb holder/hole. Cut any other connections there as well.

The cluster's board is a PCB--a printed circuit board. You might want to brush up on soldering on to them if you don't have any experience doing so. The "wires" on the board are called traces. You can cut traces with a knife in order to prevent electrical flow. I'm sure if you wanted to, you could do it just with the wiring coming to and from the cluster, but you then need to do more homework and get wires before they go into the cluster.