Tach dead?

[K25alive]

The factory tach in my '79 has stopped working. The needle is frozen at 900 RPMs. Is this indicative of a dead tach? I haven't been working in the dash or engine bay recently, so basically out of the blue it's stopped. A few days earlier it froze, but the next time I started it, it worked. A day later it froze for good.

[ray_mcavoy]

It might just be a loose connection ... check the 3-wire connector on the back of the tach as well as the power wire that plugs into the fuse panel and the ground wire (I believe that plugs into the ground buss near the parking brake pedal assembly).

These tachs use an air core meter movement so the needle doesn't necessarily go back to zero when they are powered off (or not receiving power due to a bad connection).

If all the external connections check out okay, you'll have to do some minor disassembly of the tach to check for other issues. Like a bad connection where the terminals are riveted to the tach circuit board, a bad connection where the meter movement attaches to the circuit board, bad solder joint on the board, etc.