Tachometer dead, pertronix issue?
 

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!!

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

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....

http://forums.pelicanparts.com/uploa...1285777299.jpg

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:

http://forums.pelicanparts.com/uploa...1285777588.jpg

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.