I think that I may have a bad Dual VNH3SP30 MD03A board. One motor runs fine. Other motor doesn’t run. I connected pushbutton switches to Arduino Mega board so that I push one button to make the motor run forward and other button to make the motor run backward. The green LED goes on and off normally. The red LED goes on when I push the button and dims instead of turning off when I release the button. I may have made a wiring error. The switches are wired like this: from +5V to one terminal. From other terminal to a digital pin on the Arduino Mega board and to 10 KiloOhms resistor to ground.
What power are you using? Did you connect the ground of your motor power to the ground of your Arduino? Is the power for the motors straight from power source to the controller, or do you run it through some other board (like the Arduino)?
Btw: Curiously, I’m having a similar problem. I have a VNH3 board where one channel (the bottom) works great, but the top channel does not. I have both channels hard-wired to in1==high and in2==low. One of the red indicator LEDs is half-on for the top channel, and goes full-on when I supply a PWM signal, but it still gives no output voltage. The bottom channel LED is all-off, and when supplying PWM, goes full-on, and output voltage is correct. This sounds like almost exactly the same problem you have!
This is a brand new controller, just unpacked and soldered it yesterday. I’ll try my second controller I got at the same time and see what happens.
I debugged my problem. When using the second controller, without attaching the motors, both channels came up as dim-red. When then attaching the motors and re-starting, both channels came up without the dim-red, but trying to actuate the motors made the one channel dim-red again and it didn’t actuate. Wiggling the cables showed that that motor had a glitchy cable, and making a solid solder on that end made both channels work.
So: Dim red probably means that the controller detects “broken connection” (or some other fault – possibly a short?) and the fix is to work through your connections to figure out what the fault is!
Given that I have anti-AMI diodes on these motors, I probably shouldn’t be running them the other way just to see what would happen (Prediction: Those little 1N4841 diodes will smoke before the controller detects the “short.”)