MSD/Pertronix and a working tach

stevef · stevef's Garage

Wanted to thank you all including, joe911 and jluetgen for all the input. Started my car up yesterday after the winter slumber up here in the frozen north. I have installed a new MSD box, coils, tach adapter and the ignitor (had some rework with the ignitor fit but that's another story), Started great,but no tach, the tach output on the MSD box didn't do anything. Finally ended up splicing the white wire into the Switching SCR and hey presto was it sweet. Here's the wiring diagram I used.
Thanks

pwd72s · 03-17-2003, 10:51 AM

Great diagram Steve...a suggestion to keep the diagram, pass it on should you decide to sell the car. One problem with having an older car is trying to figure out what the previous owner did...

DMX · 03-17-2003, 11:02 AM

Where did you purschase the msd ignition...? And how much?

stevef · stevef's Garage

Great idea on keeping the diagram. I got the MSD from a local performance product retail outlet in Mississauga here. "Karbelt" is a large affiliated chain here. The box cost me $355 Cdn (around $240)
I'm pleased I could post the diagram on Pelican since it adds to the body of knowledge for others to access.

pwd72s · 03-17-2003, 12:32 PM

jtkkz · 03-17-2003, 06:44 PM

Hi SteveF.

I just veiwed your wiring diagram for the MSD unit to activate the tach via alternate re-wiring.

I have a 73 and a half 911T/CIS. Recently installed the MSD 6AL with Tach adapter and coil. Sadly the Tach does not work. I tried various re-wires to get the tach to run, but no luck.

I noticed your diagram depicts a "PERTONIX's" distributor. I have the standard contact point set-up with only ONE wire instead of your system ( 2 wire). Do you have any suggestions? Another question is what's a "SCR"?

Thank you for your advise in advance.
Steve Smith
Fremont CA 94539
510-659-0992

CamB · CamB's Garage

Yeah! Great diagram.

For my '69 911T, it was the same (except no Pertronix and I didn't need the SCR - whatever that is!).

So my blk/purple went onto the white, which connected to the points and had the tach adaptor on it too.

Joe911 · 03-17-2003, 07:21 PM

SteveF - Awesome! Glad it did not take you the six months it took me to get it figured out.
Joe

jtkkz · 03-17-2003, 08:26 PM

Hi Cam-B:

Just tried your suggestion. Hooked black/purple wire to the MSD white wire which is also hooked to the white lead of the tach adapter.

PS: Open to any suggestions

Thanks
Jon

Joe911 · 03-17-2003, 08:46 PM

The switching SCR is used between the coil and the tach on 1969 S/Es and all 1970. The later cars wire the coil directly to the tach. See the picture below from up-fixen. I think it adjusted the signal in some way so the tach could read it (because of the weaker current through the points with the CDI). The 1971 and on tach were different and did not need the adjustment.

jtkkz - MSD has a web site with a diagram for points if you don't have it.

CamB · CamB's Garage

Hi Cam-B:

Just tried your suggestion. Hooked black/purple wire to the MSD white wire which is also hooked to the white lead of the tach adapter.

PS: Open to any suggestions

Thanks
Jon

I have an opinion only (sorry). It seems Porsche managed a few different tachs. My '69T one needed a coil type signal (it never came with a CDI). The '69 cars with a CDI have either a different tach (or alternatively the SCR might do the tach adaptors job?? - this would mean steve could probably remove the MSD tach adaptor (I'm REALLY guessing here)0.

I would guess your tach is no different to Matt Smith's '72 tach. He simply hooked up the blk/purple straight to the MSD tach output.

My (completely uneducated) guess is that if you hooked it up with the tach adaptor (the first time) you may have damaged the tach. I dunno. I always read these MSD threads, and have installed mine on two cars which ran simple inductive (points and coil - no CDI) ignition. Both cars (the '69T and the BMW 2002) needed the tach adaptor, but both had the tach run from the coil prior to MSD install. Matt is the only other one I know and he was too cheap to buy the tach adaptor - preferring to try and figure out a way without it. He was delighted when it worked from the MSD 12v tach output.

There are other guys who have sent off their tachs to be "modifed" to work with the MSD. My suspicion is they are only fixing the tach after the tach adaptor broke it.

Can you test your tach??? Either hook it up the old way (if your old CDI works) or try it in someone elses car? Or take it to an instrument repair place to test it?

I would gladly admit I don't know what I'm talking about!!! I just need someone to go through a bit of a test procedure.