Using the ohmmeter, find the pair of wires that has the highest resistence as measured in ohms. This will give you your common and lowest speed tap. Using each of these two leads in turn, find the pair that gives you the the second-highest resistance. This should provide you the common and second-lowest speed tap and should also allow you to isolate which of the two leads from the first test is the common.
Bonding should be by the widest practical means. Wide cable tray is effective when it is made of zinc plated steel and carefully bonded at the ends to control panel and motor frame. Zinc plated sheet steel channel is also effective. The fact that the width is folded into a U shape does not matter. A closing lid helps. Solid steel conduit bonded at both ends is effective. The spiral construction of flexible conduit makes it less attractive for RF shielding because the spiral shape forms an inductor, even with partially shorted turns.