I have been running an E420D for a couple years now, and have been slowly upgrading my setup (using aux outputs and added features). I was reading through the ECU manual again recently and it stated that the switched +12V input 1B doesn't draw much current, that it only powers up the electronics in the ECU. Various diagrams I based my harness off of did not use the constant +12V input 1A at all (or so I thought) so I did not connect it to anything. Should I be using the constant power input as well or is the ECU able to function properly with only the switched input? I have not been having any problems that I know of in relation to this issue. Thanks

 

you are good, you do not need the constant 12v