The control board is located behind the user panel and can be accessed by removing the top screws along the inside door panel and tilting the panel toward you being mindful of the wires the run down the back. The heating element can be reached without pulling the unit from the cabinet if you have small arms and know what you are feeling for. It is usually best to pull it so you can be sure and get the wires removed and reinstalled as well as securing the mounting nuts to the new element to prevent leaking. Don't over tighten the mounting nuts, just compress the rubber seals on the element enough to make a water tight seal. Get it all back together and you should be good.

Glad I could help.

Sounds like the thermal fuse has failed which is mounted to the control board. I wrote about it in my post Kitchenaid Dishwasher no Power or Lights which if you replaced the board, you already know where it is located. A bit of a coincidence that you just installed a heater kit and the fuse fails, but not surprising. If you use a multimeter to measure between the two terminals, you will find 120vac if the fuse is bad. The replacement comes as a kit and all parts must be installed to prevent this from happening again.

Glad I could help.