Tachometer dead, pertronix issue?

[joeblow]

Guys,

I have swapped in a 76' 2.7 ltr with Webers/headers etc... into my 71'. I changed the points to the pertronix unit and my original coil had died so I now have a NOLOGY M75 (CDI version) coil on her, but everything else on the engine side is original. The chassis side is all 71' with the exception of a Permatune CDI. The engine runs fine.

Per the wiring diagrams I made sure the BLK/PUR wire was connected to the points out, CDI and the RPM resister thingy on the rear board before it goes to the tach.

No tach movement at all. I checked the signal wire (BLK/PUR) at the tach and I get a nice square wave on my digital graphing meter. I even tried a trick I read in the forums to drag a positive lead over a file to simulate a square wave signal (I also tried a ground too). Still zero tach movement.

Just to ward off the possible tech issues, yes the tach is getting solid POS and NEG inputs.

First, can I assume the tach has died? Second, can the permatune fry the tach or can it even work with this tach?

Do I have some mismatching here?

Thanks!!

[ljowdy]

When I had my 2.4 engine, I installed a Petronix. My tach didn't work so I called Petronix in San Dimas, CA and found out that their instructions were wrong. I can't remember what they said but try calling them at (909) 599-5955

[joeblow]

I talked to Pertronix but they kept telling me to re-check my wires, I have done that. Then he said I could put a capacitor in-line with the tack lead but that is to reduce noise, I have nothing so I don't think noise is the issue. I found the following on Pertronix's site but it leaves off the 'Speed Switch' from the diagram. See attached....



Does anybody know if this is correct to no longer use the speed switch? Right now I am wired up exactly the same except the speed switch is in the loop as well. The car runs but no tach?

Here is the cropped section of the factory wiring, #9 is the CD box, #11 is the Speed switch, #5 is the Points(Pertronix), #6 is the Coil:



The only difference is that the Pertronix needed a power wire so I added that to the rear fuse box. Everything else is as it is in the diagram. Also I have a NOLOGY M75 coil as my original was dead if that matters.

Any thoughts guys? I am leaning toward the tach being dead but it was a working unit before the restoration. I would like to crack it open if I could get some pointers.

By the way my Snap On Digital timing light reads RPMs fine.