yep, definitely time for a trigger master!
I'll even install it for a bag of .28s! ;)

other possibilities (though i know that it has nothing to do with your electrical) is if your using bearings and the gears arent shimmed properly, they tend to press against the back of your selector plate, which either causes it to bend slightly and when pressed against the body of a receiver, create alot of friction. If its not free to move, your selector will not function properly in semi, but work on full auto. I mention this because even though it has nothing to do with your electrical, it is the other 1/2 of the parts involved with the function of the selector.

Why didn't you invite me over for beers, i could have looked at it chief:)