Why not try hooking the tach signal wire directly to the points. If your tach was upgraded to more modern circuitry at some point it could be that the Bosch signal conditioner (I assume that is what your are calling the rpm transducer?) won't provide the correct pulse. It could be that it will drive from a weak 12V square wave instead. Fred
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Originally Posted by missoula911
I have a 1971 911 E which is giving me tach issues. I recently changed the ignition system from a Permatune system back to the original Bosch CDI system. While this took care of my stalling issues, I have not been able to figure out the Tach problem I am having. I hooked the original CDI unit up and wired it correctly but my tach is not working correctly. It registers a RMP but it floats and flutters and is seemingly gives an incorrect reading. The Permatune system had a white wire which was connected directly into the tach wire just below the CD box. This connection bypassed the RPM Transducer and other wiring in the fuse box area in the engine compartment. I have my father's car to look at and it seems that all the original wiring is hooked up right. I took the RPM Transducer out of my car and put it in his to see if this was causing me the issue but it worked just fine in his car. I have traced all the wiring through the back harness and it seems to be working correctly. And with the Permatune system in place, the tach worked perfectly well. I took the tach out to see if there seemed to be something out of place there but everything appears to be fine based on the wiring diagram. Any help with this issue would be greatly appreciated. At this point I have disconnected the wire for the tach that runs off the coil so I do not damage the tach. Thank you in advance for any help or thoughts any of you might have!
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