LS1 ECU to 240SX S13 speedo

There has been a lot of mis-information on the web about exactly how the S13 gauge cluster operates.  Hopefully this article clear things up.

First of all, everyone that said 2k, 4k or 8k ppm for the gauge cluster is wrong. 60Hz AC sine wave, ~3V p-p into Y/L with Y/B grounded gave me 13mph.  This means the gauge cluster needs 16,000 pulse per mile by the following calculation:

60Hz * 3600 sec/hour * 13 mile/hour = 16,000 pulse / mile

You also don’t really need a Dakota Digital box, unless you like to blow $70.  Reason being the LS1 ECU can be configured using HP tuners to give the correct 16,000 PPM output.  (VSS Output Pulses per mile)



However, the LS1 ECU send out a DC square wave, 12v p-p.  It looks like this:




The s13 gauge cluster needs to see 0 crossing on the Y/L line.  Instead of using a dakota digital box, go to radio shack and build this.




The  circuit is not all that complicated.  I crammed it all together, put some heatshrink tube around it and tied it into the main dash harness.














Voila!  Although it is not a perfect sine wave, the s13 gauge cluster will happily give you an output using the following waveform.



22 thoughts on “LS1 ECU to 240SX S13 speedo

  1. Love the write up! But I’m a little confused about 2 things. Isn’t the speedometer wire Yellow\Blue (signal) and Yellow\Black (ground) on the S13? Also, do you hook the cap’s (+) to the LS1 PCM speedo out and the (-) to the Y/L in your diagram? I’m a software engineer, not an electrical engineer 🙂

  2. You are correct. Yellow/Blue is the signal, but Nissan refers to it as Y/L (Yellow/Lavender). Y/B = Yellow/Black.
    As far as the polarity, I think your way will work. I found some random cap at radioshack that had no polarity and it worked. Like you, I’m also software not electrical. Trial and error 🙂

    1. Trial and error with cap polarity could be an explosive combination, don’t want to let out the magic smoke in the wiring harness if you know what I mean. I’m assuming I’m right, but my arrogance has gotten me into trouble before, I guess I’ll stop by radio shack and try to pick up the same cap you picked up. I appreciate the quick response!

      1. Let me know how it goes. I also vaguely remember swapping the Y/B and Y/L at some point, but I’m not sure. If you do it let me know, I will update this guide.

  3. Nice attention to detail so far, keep it up buddy…btw, aside from the usual nissan fanboy sites, is a pretty tech savvy site with good writeups regarding heavily modified turbo KAs and some LSx swap members as well. Take care!

    1. Yeah, pretty much anything on nico is going to give you cancer. I haven’t looked at KA-T, but if its half as technical and helful as the posters on LS1Tech it’s going to be good.

    2. Thanks for the encouragement! I used to frequent KA-T, but too many ghetto ebay turbo projects. I find LS1tech and silviav8forums pretty helpful these days.

  4. I’m glad too see that some else has figured this out. I went a little overboard and used a 2N4401 NPN switching transistor and an audio transformer from Radio Shack. I used the secondary coil as the primary and placed a ~500 ohm resistor at the collector. This gives a pulse current of ~27mA through the transformer and will produce a wave like yours, but at around 8Vpp. I did a simliar thing for the tach, except I’m generating 100Vpp.

  5. I tried this, but it did not get the speedo to work. Can anyone give a better picture or details ? I went to the plugs on the back of the speedo head to get the correct wires, and sent new wires to the VSS output at the ECM wire (NEW painless wiring harness).

  6. If you mean Yellow/Black wire, then yes it is in the centre plug on the back of the cluster. The other wire is Yellow/Lavender(blue). Make sure you have the cap installed in the correction. Google Images will show which end is positive. I won’t know if mine works until I get the ECM set to 16,000PPMs. I had it set to 66,000PPMs by mistake.

    1. Randy, Let me know if you get it to work. I tried that wire but got nothing. I have mine set to 16000 ppm in hptuners. Also tries grounding that wire but it threw a code for vss.

    2. Never mind Randy, It Works!!! I think when I grounded that line out I had to reset the PCM for it to put out and output again. I do t know??? But it’s working now!

      1. I’m very glad to hear it worked. I have just bought insurance for my car, and will soon book an appointment for the ECU reset to 16K PPMs.

  7. So I’ve had this mod done for about a year, and it works great, but I’ve been having an issue with the speedometer that I’m not sure is the result of the mod or a bad speedometer.

    Watch this video and LMK what you think.

    At speeds above 75mph, the speedo drops to 0, then when you decelerate below 75mph, the speedo pops back up and starts working again.

  8. This is really interesting, You are a very skilled
    blogger. I have joined your rss feed and look forward to seeking more of your fantastic post.
    Also, I’ve shared your web site in my social networks!

    1. Good at math? Do you even apply yourself? This is like a 5th grade math problem.

      There are 0.62 miles in a kilometer, (a kilometer is 62% of a mile) so if you multiply your pulses by that then you get the number of pulses in a kilometer.

  9. Great info no here. If your having issues with your speedo dropping out at higher rpm with this mod reverse the polarity on the capacitor.

  10. Hello, Im lookimg for a little help with this and a 300zx Z32 LS1 swap. Could you send me an email with your contact info?

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