Swapped my dummy lights in my 84 v6 camaro to a cluster of gauges from the boneyard. So far I've get everything except the tach to work on my HEI 305. I've tried running a power, ground, and tach signal to the back of the gauge and it always jumps to 4500 rpm and stays there until I take offthe power wire. this is my second boneyard tach with similar results. Any ideas?