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Can’t activate main relay EMU BLACK

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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So I just finished wiring up my EMU Black for my SR20DET. Upon testing all of my outputs I realized that the power for my injectors (which comes from the main relay) was not present. I realized that the relay was not turning on and certain sensors along with my injectors had no power going to them. I de-pinned the auxiliary wire from the ECU which switches on the relay to find that it does indeed supply 12v when I turn the relay on in the EMU software. I then tested the relay by supplying power/ ground and giving power to the 12v switched wire to confirm the relay was working. So both sides of the circuit are working, ecu is providing 12v and relay is turning on when supplied with 12v from battery. But for whatever reason when I plug the pin back into the relay it doesn’t turn on and the voltage at the wire becomes 0.1v more or less. Does anyone know what might cause this? I am completely lost as to why it wouldn’t work when plugged in if both sides of the circuit are working fine. Any help is appreciated

Most ECUs want to switch the ground side of a relay trigger. So while you will measure 12V, they will not normally drive 12V, it is just "floating" to that voltage with no current capability.

My understanding is that the EMU Black can switch both sides of the relay hence the "invert output" option when setting up auxiliary outputs. But if what you state is true then I could easily wire the positive side of the relay to battery power, and have the ECU switch to ground for the relay to kick on. I'll go ahead and try this when I get home from work, seems to me that it would do the trick.

Did you try both "normal" and "invert output"?

Yes, when the output on the ECU is "normal" while the auxiliary output is de-pinned from my Deutsch connector (from ECU to Relay), the pin for the auxiliary output reads at about 0.1v.. When I select "Invert output" in order to switch from ground to 12v it does exactly what it's supposed to, the pin reads 12v. So ECU is indeed providing 12v when I "invert output", so I go ahead and re-pin the Auxiliary output to the Deutsch connector. When I do this and I "invert output" the pin comes back at 0.1v instead of 12v like it does with the auxiliary output de-pinned from the Deutsch connector.