75 Tachometer Problem

[Eric F.]

I'm trying to troubleshoot my tachometer because it isn't working. There are three wires connected to the rear of the tachometer; they are black, pink, and brown. The wiring diagram shows the black wire to be ground. The pink wire is a constant 12-volt supply and the brown wire goes to a filter on the manifold and from the filter to the "tach" location on the distributor.
With the ignition turned to on and the engine not running I checked the wires; the black is a good ground. The pink is 12 volts and the brown is also 12 volts. Should there be 12 volts at the brown wire? This wire carries the signal from the distributoir to the tachometer. I can't find anything in the wiring diagram showing the voltage of the brown wire and/or when it should have that voltage.

Can anyone help me with this problem?

Thanks in advance.

[Jim T.]

Re: 75 Tachometer Problem

I cannot help with the trouble shooting since my 68 and 70 has mechanical tacks, however www.mamotoworks.com/corvette has the parts to make your tack work. The circuit board in the tach and filter are now available. To remove the tach needle from yours, gently turn it counter-clockwise and install gently pushing it on. I don't know if the 75 service manual has the procedure for testing the tack filter and circuit board.