Ok, found it!
PID: 84
Programs -> X10 -> "Set to 100% when switched on"
I thought I was using it, but it's turned off. I don't know if it's been moved since I installed HG last but you should be able to find it in that location or something similar. Worst case, you can search through the modules.xml file and locate it that way. If for some reason it's not installed with the stock build anymore, you can use the attached export. I'd recommend using the built in one if it's there.