|Posted by Duane Pankhurst on 08/24/05
Scanned from Stewart Warner Factory Design Drawing
|Posted by Ken Scobel
To test the tach itself, you can use either a flashlight battery or a camera battery to simulate the sending unit output. Unplug the sending unit and then connect a jumper to the yellow wire in the dash side of the harness and the positive post of the battery. Ground the negative side of the battery to the dash. Your tach should respond based on the following chart.
|Posted by Greg Garner (RealTime Eng.) on 06/10/03
The voltage regulator should not have affected your tach. If your car is a '66, then you have a tach sending unit under the glove box that could be bad, or the tach itself could be bad, or it could be that the tach is not correctly hooked up. You can see if the sending unit under the dash is there. If you have a voltmeter, check for continuity between the gray wire on the sending unit and the - side of the coil. Then check the output of the sending unit (yellow wire) when the car is running. You should have around 1 volt or a little less at idle, and it should go up as the engine is revved up. The yellow wire is connected to the back of the tach. If there is no voltage then the sending unit is bad. I am selling replacement sending unit boards for $75 if you want one.
If your car is a '67, then the tach has two wires (twelve volts, and minus side of coil) plus ground. Check and see if the screw with the flag connector has continuity to the minus side of the coil. The long screw with the insulator should be connected to +12 volts, and then frame of the tach should be grounded. If your 67 tach is hooked up correctly and does not work, then the board inside the tach is probably fried. I have succesfully installed one of my boards into a 67 tach with some trimming of the board and drilling 5 holes in the board. I plan on making a new board in a month or so that will fit the 67 tach with no modifications.