Hot bed UM1

[sethreign]

I have uploaded marlin firmware to support a heated bed, soldered the 4.7k in place. I use my ulti controller to heat the bed but the red led on the board will not light/flash witch means I can turn on/off my relay to control my heat bed.

any help what mite be wrong?

[soofle616]

Did you reverse the polarity of the power to the heated bed? The bed doesn't care which side is + and which side is -, it's just a giant resistor but the LED will only work in one direction.