Is there a way to bench test an original 69 XR7 tach while I have my dash out? Mine is currently not working, as far as I can tell, but would like to know if there is a way to bench check it while I have things apart.
Thanks
I would send the tach to Rocketman for a 3 wire conversion. This is as close to a no-brainer as we’ve got here in the Classic Cougar world.
You can test the original tach with a square wave generator. Most people do not have one of those. As an alternative (less exacting) you can use a ballast resistor (or the pink resistor wire in the harness) with one lead connected to 12V and the other lead connected to one of the tach wires. The free wire of the tach intermittently touch to ground. If the tach is good, each make/break with ground will cause the tach needle to jump up a little. This would indicate a good tach. No movement would be bad. Also, check for continuity between the two tach leads, if you measure high resistance between the leads (or they measure open), this also would indicate a bad tach (tach transformer to be exact).
Hope this helps.
Regards,
Robert
Robert,
I tried the ballast trick you mentioned, and if I did it correctly, nothing happened. No jumps in the needle. Also did the continuity test. It read infinite and did not drop down to a low ohm reading. So in a nutshell, looks like a bad tach. Looks like I will be sending it out to Rocketman soon. Thanks for the help.