Tach Question

[CT Stang]

I have a 1992 5.0 and when I start the car the tach goes right up to 3000 rpm's and wont move until I rev the car over that.When the car gets shut off the tach goes back to 0 where it should be.Any ideas what could be causing this?Thanks

 

[89nascar]

my 92 5.0 tach has the same problem i think it is the green diode with the black stripe at the right of the pictures , it reads no resistance in both direction just like a soild wire? can anyone can tell me what this componet is ? thanks

 

[89nascar]

i did some checking with the ohmmeter today and found out that one of the nuts that connects the circut board to the motor was not making a connection between one of the 4 treaded posts and the circut board, may have came loose from vibration, now the tach checks out ok. this may be the problem with all the tachs that quit working