I am trying to replace a 3 gang lighting swirch with a 3 gang dimmer. The old wiring had 5 black wires wound together and thr switches wired up only with red wires; taking this over to the dimmer is proving problematical! I have tried most combinations but no joy; Presume the common red goes to the variable, single reds to L2...but have 4 black to contend with and three holes...any advice? thanks!