The first thing I would do is check to make sure the dash is grounded properly. The safest way to do this is make a new ground wire from the dash to the body. I assume this is a factory tach?
Next, as you suggest, check the connection at the tach.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
The first thing I would do is check to make sure the dash is grounded properly. The safest way to do this is make a new ground wire from the dash to the body. I assume this is a factory tach?
Next, as you suggest, check the connection at the tach.
Cheapo aftermarket tach........... works fine w/o hdlites on.