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Old 05-26-2014, 04:40 PM   #1
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Default I'm stumped - Trouble wiring Wells TPS

I've been staring at wiring diagrams, wishing I was dead for the past few hours. Please help.



I have a 1.6 manual transmission Miata with an AEM Plug-and-Play EMS (that part's important).

I have installed a Wells TPS just as is described here:


That means that I have connected the wires from the Wells TPS to the factory TPS plug. So, from that plug up to the ECU, the wiring is all stock, and that's where my problem comes from.

Per the above configuration:
  • the red wire from the Wells TPS connects to the red wire on the stock harness, which runs to pin 1N (closed throttle position switch) on the ECU.
  • the black wire from the Wells TPS connects to the black/light green wire on the stock harness, which runs to pin 2D (sensor ground) on the ECU.
  • the green wire from the Wells TPS connects to the light green/white wire on the stock harness, which runs to pin 2L (WOT switch) on the ECU.

It's my understanding that if you install it this way and you have a Megasquirt setup, the wires are fine, but you make internal changes to the ECU in order to shift around where the signal is going to. So, I assume, that has essentially the same effect as swapping wires at ECU harness.



The problem is that I have it installed precisely as described above and the AEM ECU just flat-out doesn't "see" the signal changing as the throttle is opened or closed.

So I took a gander at the AEM ECU pinout, and it is essentially identical to the factory ECU pinout, only pin 2M (which is blank on all of the popular pinouts floating around the forums) is listed in the AEM pinout as TPS sensor input. Sure enough, I checked the factory wiring diagram from the Mazda service manual, and it shows the wiring for both the manual and auto tranny versions of the Miata, and 2M does indeed appear to be an input for the auto's TPS.

Okay, so that's all fine and dandy, and I now know that I need to swap out one of the wires (either 1N, 2D, or 2L) at the ECU harness so that its signal is rerouted to pin 2M on the AEM ECU.

The question is, which one?

I think that the answer is that I need to take the wire at 2L (on the harness near the ECU) and remove it from its pin, and then insert it into 2M. In other words, the green wire from the Wells TPS is (I'm assuming) the variable position signal. It connects to the light green/white wire at the TPS harness, then that light green/white wire runs to the ECU where should get swapped into pin 2M, which is where the factory automatic tranny ECU would be looking for a variable TPS signal.

Does that sound right?
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Old 05-26-2014, 04:49 PM   #2
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Also, notwithstanding the above question, a normal three wire TPS on a normal car would have ground, power, and a signal output wire, right? Therefore, the Wells TPS wires of black, red, and green, would likely translate into ground, power, and signal output, respectively, right?

As such, if I were never able to determine which factory pins served which purpose on the stock on/off manual tranny TPS, I could always just run sensor ground, ECU power, and then connect the signal output wires through a custom subharness provided that I hook the signal wire to the right pin on my AEM ECU, right?
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Old 05-26-2014, 04:51 PM   #3
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Also, check out this thread: https://www.miataturbo.net/megasquir...ictures-23979/

Am I wrong or does Braineack wire his different than cardriverx? If so, how does it still work?
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Old 05-28-2014, 05:54 PM   #4
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Anybody?
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Old 05-31-2014, 12:11 AM   #5
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I'm open to any feedback.

I am pretty sure I am right, I just don't have a data cable to let my laptop talk to my ECU to check the success of my wiring harness changes, so making the changes, checking for bugs, and the changing stuff around again isn't really an option.

Speaking of which, if anyone has any idea where I can get a USB to serial cable that will actually work on a Windows & machine, I would really appreciate a suggestion. I have purchased a couple of them only to find out that the XP and Vista drivers which are supposed to work on a W7 machine do not, in fact, work as advertised.
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