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Shift light (PWM) resets on restart to low side


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Hi. I found the shift light output which I have set on Aux 5 defaults back to low side when the ecu is restarted. I require High side however it won’t save the setting. The driven source is 36 ohms so should be under .5 Amp draw 

Is this possibly a firmware glitch? 

My firmware is:


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How did you use cam switched to trigger a shift light? I'm guessing you dont actually use cam switching and were happy with just on/off for the light?

For the link guys: If any of the aux outputs 5-8 are set as "shift light PWM" then it lets you select high side drive (as do most other functions on those outputs), and from memory it did actually work until the ecu is power cycled and it changes itself to low side drive.  Would be nice if the firmware either worked, or at least didn't let you set high side drive if its not going to work anyway.

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  • 1 year later...


I'm not sure if my issue is the same or not,

wrx4+ pluggin, I wired an LED band to act like a shift light, 120Ohm resistance, on the aux6.

Wired as high side driven, ECU to LED to GND. I always get the led turned ON when I select the paramter Shift light (PWM).

I tried to go in test mode ON, if I select lowside and chenge the polarity, the LED turns on and off accordingly. Now if I select highside, LED is always ON whatever the selected polarity.

I that a firmware bug, or didn't I catch a specificity of this shift light function?

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There is no highside drive hardware on most of the plug-in ECU's (a couple of exceptions on specific models only).  It will work in test mode as there is a weak pull-up resistor to 12V, so when "off" it will output 12V.  I think you will have to re-wire your lamp so that it is connected to 12V and the ecu controls the ground side.

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  • 2 months later...

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