I have an in dash factory tach that did not work when I purchased the car. I checked the wiring and found the tach lead connected to the positive distributor wire. What damage is done to the keep this from working now. Will I need to replace the tach, circuit board, or something else. I haven't removed the board to check for damage yet.
As I remember the brown wire does go to the neg. term on the coil which is the dist. primary wire. Could be some damage in there. I had one of these years ago that quit. I took it to a electronics repairman, he took it apart and check it real quick. There are a couple diodes that apparently control/protect the rest of the circuit. Cost about 50 cents each. With luck you can get yours checked and fixed pretty simply.