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Thread: Gray "ECU signal" wire under dash

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    Gray "ECU signal" wire under dash

    So I got around to removing the pesky CARTEK mph converter module (car is now in an EU country using KMH again) and I am left with one wire which I'm not sure where it goes to. It's a gray unmarked wire which seems to have a factory sleeve. It lead directly to the mph converter chip behind the gauge cluster, and it was attached to the "ECU output". Does anybody know where that wire is meant to go to? I'm guessing it comes from the ECU, as I can sort of trace its sleeve going down behind the radio on the right side. Does it usually lead to the other gray wire coming from the speedo plug? I noticed it also had a gray wire, but it didn't appear to be cut anywhere. Here's a few pictures of the mess.

    120302571_625141211501753_4587357612324206337_n.jpg120345507_3503720596332835_4960210437350038210_n.jpg120401263_253803039314490_8103948892110796228_n.jpg

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    vehicle speed sensor wire from the ECU is white with a green trace, so it's probably not that.
    '97 Manual Legnum in silver with some subtle mods

    My first VR4 - '97 Legnum Dark Green & mean ...it was love at first sight - now sold

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    Correct, that wire was cut and the blue/yellow wires were lead to the mph converter. I rejoined them so I got my speedo back, but now I'm left wondering if this gray wire is entirely standalone or if it does in fact lead to the car's original harness somewhere. Maybe they just spliced it onto the ECU plug? Trying to save myself of removing the kick panels and pulling the ECU.

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    I've not been able to dig out a grey wire on the original wiring diagram - but that's not to say it's not there, just without knowing what circuit it's for, it's difficult to find!

    However, on the below image, which comes from the guide on how to change to the High Contrast gauges, there's not a grey wire listed. Which pin is this grey wire in, and maybe then we can marry it up to one of the pins listd below, and I can find it on the original wiring diagram

    HCTacho2.jpg

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    Confused's Avatar

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    There also isn't a solid grey wire that goes into the engine or transmission ECU.

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    The diagram appears mirrored, as the vertical connector is actually on the left side when looking at the cluster. Anyhow, you can definitely see the grey wire in my second pic, I have a red arrow pointing to it. Lighting doesn't do it justice but I 100% guarantee it's grey and not white. In which case, if we follow the diagram, that puts it as Pin 11 on connector B, which says it's not used. Usually when pins or connectors aren't used, they don't even have a wire going into them, so I don't think the diagram is correct, for my case at least.

    I'm starting to think it's simply a standalone wire that they ran specifically for the converter, which gets the ECU's calculated speed signal and matches it with the converted speed so the needle doesn't go crazy. That's my theory at least. I will go on a drive later and confirm through evoscan and a GPS whether all indicated vehicle speeds match and are in KMH. Thanks for the help!

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    Ah, yes, that diagram is looking at the back of the cluster, not how they're sat in the car. This photo probably explains better the difference!

    HCTacho1.JPG

    This info was from a Dutch forum thread HOW TO: Upgrade to High Contrast Dash, and I think was more geared towards the EUDM models, not the VR-4.

    If you do manage to find where that wire goes, would be very interested to know, and maybe I'll get round to doing the pinout as it is for a VR-4 rather than a EUDM model.

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    Well I found out by trial what the grey wire does, but I have yet to determine where it comes from and where it leads to.

    Went for a hoon earlier to check how the new coolant is and if the new boost gauge works (steady 0.4 bar which is great if I've read right?) and even though my speedo does work in kmh now, after checking the log in Evoscan, I could see that the [Speed] data was nil. Whilst a few days ago, before messing with the MPH converter, the logs did show speed date albeit in mph.

    So, if we put two and two together, it seems like the ECU is currently not getting a speed value. So help me get this straight: Does the VSS (in my case I believe it's internal in the auto case) send signals through two different wires? One to the speedo, and one to the ECU?

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    What age is your car?

    The speed signal does split but I'm not sure where and as far as I know it is never grey.

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    June 2000 is the build date albeit first reg in UK is 2002. It's a facelift Type-S auto Galant estate with AYC and the gray interior pattern. I will be removing the kick panel tomorrow to see exactly where it leads to, I am guessing either spliced into an existing ECU wire or directly to one of the ECU pins. I am 99.9% sure I didn't see its other end cut anywhere on the gauge's harness.

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    You have a second facelift, so your chassis code will likely be 04xxxxx. That means you don't have a vehicle spčed sensor. I think the tcu outputs the speed signal based on gearbox shaft speeds. Try askin @elnevio as he has a similar aged car and has been playing with speed converters recently.

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    Yeah, I reckon you have to chase where it goes to the ECU. I note that your convertor was equipped with a grey wire to go to the ECU, from looking at your pic. Maybe it goes to the white-green wire in pin 16 of the fourth connector for the ECU, i.e. the one you cut to remove the 180kmh limiter. That way, it would still feed a speed back to the ECU, possibly in mph, so the limiter moves to 180mph instead, and preventing the occurence of a fault code.

    Most converters it seems have five wires. In my case (I got the same one as Nick), the fifth wire, which happens to be green, is unused and you just insulate and tie up out of the way. I further wonder if the grey wire in your case didn't even need to be connected for the same reason. The convertor for the VR-4 only needs ground, +12V, speed signal in, and revised speed signal out to speedo.

    However, as I have discovered, you can't fit the speed convertor in the late facelift in the same way as earlier cars. With plenty of help from Confused, I found that you can use the white-blue wire at pin 7 of connector C-83, which is behind the stereo. Yes, the speed signal to the speedo is white-blue, not white-green! It changes colour at C-83 (or seemingly in my case just before, possibly where it splits off the loom, as mine was white-blue both sides of the connector). It will be interesting to see if this wire is involved in any way in your case.

    C-83 is the connector on the right and pin 7 is the fourth down with the white-blue wire coming out of it:

    20201001_125202.jpg
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    I appreciate you guys' help.

    The way I see it; before I messed with it, the ECU was in fact getting a speed signal. Now, after cutting the grey (ECU Output) wire, the ECU doesn't read a speed value anymore. That grey wire simply must be the wire that now carries the corrected speed signal to the ECU from the converter. On some google pics I noticed that these converters come with wires pre-attached to them, including a grey wire. They appear to be no longer than 3 or so inches. So, by that logic, if I pull back the sleeve over the grey wire a bit, it should show where they soldered to the original wire! Then I can compare again with the gauge connector wires and see what's what.

    You are also correct in that on my car, the white(blue striped) wire is the one that carries the speed signal from the gearbox to the speedo, so it wouldn't be that.

    I will be confirming all this tomorrow and let you know!

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    Right so here's the situation. The grey wire coming out of the converter chip (ECU output) was in fact soldered to random non-factory wire. Then that wire lead all the way down near the ECU connector 4, and was soldered to the VSS speed signal wire directly; the white+green stripe wire and two silver dots. As far as I've read on the forum, that's the wire people cut to eliminate the speed limiter. However, as we have found out, it also cuts signal to Evoscan and any other diagnostic/logging tool through the OBD port. I really couldn't see where the original end of the speed wire was and I gave up. As far as I'm aware, other systems such as the AYC gets its information through the ABS sensors, so it wouldn't affect it.

    I'm going to leave it like this for the moment, but I really do wonder where the other end of the white-green (2 dots) wire is. I saw some other shady stuff and wire splicing going on at the other ECU connectors...

    120504430_339033047331958_7159577573679026348_n.jpg120577966_4459245184117274_6707362454798506997_n.jpg

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    The white-blue wire is the white-green wire, i.e. the signal from the VSS. It's just that the colour changes to white-blue before it heads up to the gauges.

    You have a plastic-cased ECU - what age is your car?

    I suspect that the other end of the snipped white-green wire will be taped back into the loom.

    Incidentally, does your shady wiring elsewhere on the ECU plugs happen to look anything like this?

    20201006_175319.jpg

    My initial thoughts were that the three thick white wires involved were all purposely earthed out! They are the wires for the Lambda sensor, knock sensor and traction control trigger and all lead to separate thick green cables, assumedly multi-core (you can just see one at the top of the pic) although I haven't yet removed the grey tape to see what is definitely going on under it.

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    Quote Originally Posted by elnevio View Post
    The white-blue wire is the white-green wire, i.e. the signal from the VSS. It's just that the colour changes to white-blue before it heads up to the gauges.

    You have a plastic-cased ECU - what age is your car?

    I suspect that the other end of the snipped white-green wire will be taped back into the loom.

    Incidentally, does your shady wiring elsewhere on the ECU plugs happen to look anything like this?

    20201006_175319.jpg

    My initial thoughts were that the three thick white wires involved were all purposely earthed out! They are the wires for the Lambda sensor, knock sensor and traction control trigger and all lead to separate thick green cables, assumedly multi-core (you can just see one at the top of the pic) although I haven't yet removed the grey tape to see what is definitely going on under it.
    Yes! My wiring near the ECU connectors looks almost identical, with the same grey tape and thicker white wires which have smaller black ground wires going inside (but I haven't torn it up since I didn't want to dismantle more stuff). It's June 2000 car, so as somebody mentioned, a 'second facelift'. It also seems to have the good ECU since I could easily connect to it through Evoscan and a cheap VAG cable.

    So what you're saying is, the VSS has a single wire coming out of it which is white-green (2 dots) and goes to the ECU, but somewhere along the line, it splits off into a white-blue color and heads up to the gauge cluster? If so, theoretically, in the future could I just splice a new wire from between the white-green at the ECU (pin16) and up at the speedo connector? I believe there should be a way to completely disable the speed limit through ECUFlash anyway, and I'd like to get my speed reading in Evoscan back.

    We need someone with a full VR4 harness laying around to see exactly where both wires join.

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    I assume yours doesn't have TCL? Mine does, so is exceptionally unusual for a facelift, let alone a second facelift (mine is 2001), so I had also wondered if it was anything to do with that.

    Yes, I did think that you could use a wire from the speedo cluster to the white-green wire on the 4th ECU connector as the means of getting the signal there. And you already have a handily placed grey wire and random wire combo that runs between the two points! And yes, the speed limiter can be flashed higher.

    The join is somewhere near connector C-83 behind and below the stereo that I've mentioned earlier.

    IMG-20201001-WA0009.jpg

    IMG-20201001-WA0008.jpg

    Thanks to Garry for the pics. Note that connector C-81 seems to be absent, hence C-83 actually appears to be the right-most one (you can see the space where it would go though).

    As mentioned before too, the wiring diagram says that the VSS signal wire should be white-green one side of C-83 and white-blue the other. Mine is white-blue both sides, so suspect that the colour actually changes at junction 21. If this is the case across the board for VR-4s, then the wiring diagram should show W-L in between J21 and C-83 rather than W-G.

    Anyway, I reckon the wire would run something like this:

    20201007_092530.jpg

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    Tell you hwat buddy, that makes perfect sense. I might as well connect that grey wire to the other one behind the speedo as you say; it would be more helpful to have a speed signal for logging, at least for now.

    Thanks to everyone for the help and diagrams!

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