Extruder Troubleshooting - No "Enable" Signal

Hello everybody!
I am in the process of converting a Wanhao i3 to RAMPS 1.4 with DRV8825s. Everything is working now apart from the extruder motor, which is not under any circumstances seeing any voltage across either coil. I have swapped my DRV8825s around with no effect.

I checked voltages on all the pins of the E0 driver, and the only thing that appears out of order is that the Enable pin is not going low (0V) when I activate the stepper in Rep-host. All other drivers are getting 5V when disabled, and going to 0V when enabled.

Any ideas? Thanks!

Also worth noting, I have tried multiple Arduinos. No change.

Well, it appears that my Arduinos are not changing the state of D24, which goes directly to E0-EN.

I checked that the 10k pullup resistor on the RAMPS (R16) is good. I retouched all the solder joints back to the Arduino. However, when I disconnected the Arduino itself, I see can see in isolation that D24 stays at 5V when the extruder is called to activate.

I guess this is a firmware issue, although I used the preconfigured firmware available on the Wanhao group. I will have to fight with it a while longer, I guess.

Make sure you have the correct board set in firmware, allso check pins_RAMPS.h #define E0_ENABLE_PIN 24