This is a tachometer circuit from an early 80's Honda accord. I twisted the yellow and blue leads together and was able to get the tach to work (retrofitted into another older Honda that only came with a mechanical tach option). The twisted pair was ran off of the negative of the coil and the black was sent to ground. This caused the pink (resistor?) to overheat to the point that it partially burnt the PCB and melted the solder off. I can easily enough re-solder the circuit but I want to know where I screwed up at...I'm thinking that either the blue or yellow lead needs to be the switched 12v power source. Can you guys point me in the right direction? Here is the reverse side.