I don't know the answer, but some newer tools have a "black box" inside them to prevent bypassing safety features- like wire tying one trigger/switch. The newer Metabo right angle grinders have a safety feature that prevents it from starting if you lock the trigger, like with a wire tie, and then plug it in. This makes sense because you don't want to plug it in and have it immediately running if the trigger is tied closed, or it somehow got jammed during storage. I did a design at work for a specialty machine with a Metabo grinder and needed it to stay powered up with the trigger locked- we would turn it on externally. We wire tied it closed but that didn't work- it didn't run when you plugged it in. "oh, that makes sense". So I gave the grinder to the electrician, and he couldn't figure out how to conquer the internals of the black box with limited time - so he completely removed and bypassed it. Which was fine, but we lost the variable speed control; this wasn't a big deal because I wanted to use it on the 5/6 setting, and just used it on max speed instead.