Pertronix/Tacho issue... Could it be?

[Treefiddy]

Starting off by saying hello.. First post but have read a lot. I recently purchased a gem 1973 240z. The car is nothing short of amazing. Super clean original, working dealer installed air, no rust, has been repainted.. a really lucky find and as fate had it, found just a few miles from my home.. I'm building it to a daily. Will be sure to post some pictures.

My problem. 

I have installed pertronix ignition with a 1.5ohm coil. I have wired it precisely to the John Hull wiring diagram with the BR wired in.. My tach no longer functions. It worked perfectly before the swap. All wiring appears to be factory with the exception on the red and black pertronix.

What is different for my car.. I have 3 B/W wires and no G/W wire.. Two b/w wires for the BR and the 3rd connected to positive side of the coil.

One of the b/w wires that has voltage when the ignition is in on is connected to the BR with the red pertronix wire. Another B/W wire, which will not reach the other side of the BR, is connected to the BR.. Hope that makes sense. I have the 3rd B/W wire, had no voltage with ignition in on, connected to the positive side of coil. The short B/W wire and the B/W wire connected to the coil have continuity. 

In the morning I'm going to start unplugging B/W wires and find which causes the engine to die and verify that wire is connected to the BR.. I'm thinking I have verified this wire but I'm at the grasping stage..

While reading others with a 1973, some have discovered they have the newer 3 wire tach.. what would be the proper way to hook that up?

Any help is appreciated and sorry for another tachometer thread.. 

[Treefiddy]

Ok, new discoveries this morning.. I peeled back the tape off the group of wires and found my Green/White wire.. I have an identical setup like this post:

Post 14 in this thread. I have pictures but photobucket is now a pay site? ha

To sum: My Green/White wire spliced with 2 Black/White wires. I had one hooked to coil side of BR and the other hooked to the POS side of the coil. This removed the Tachometer from the loop by basically connecting the BR directly to the POS side of the coil. I'm fairly certain this is how it was hooked up factory. My car is a 7/73 production. I believe I have a 3 wire tach because of this and also evidence is 3ryce had the same wire setup w/ a 3 wire tach.

I have one unaccounted for wire in this bundle.. It is solid black. This wire appears to come from the same area as the Green/White wire(in the same bundle from the cab of car). I also still have the black wire that connected the old points to the NEG side of the coil that I thought terminated between the distributor and the coil. These two Black wires are spliced with one end originating from the dash area and other two going to distributor/coil..

I'm thinking this black wire is what the Tach got its signal from off the Neg side of the coil..

If it is indeed a 3 wire tach, all it needs is a wire from the NEG side of the coil? Am i crazy in thinking this? Does any of this make sense? lol  I've worked all night and just home and think I may be on to something here. Thoughts?

 

 

 

[RCR Z]

I had a very similar problem with my ‘70. Check out this link for the fix per Ian at Pertronix:
Petronix Ignition Module
https://r.tapatalk.com/shareLink?url=https%3A%2F%2Fwww%2Eclassiczcars%2Ecom%2Fapplications%2Ftapatalk%2Findex%2Ephp%3F%2Ftopic%2F59838-Petronix-Ignition-Module&share_tid=59838&share_fid=83168&share_type=t


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[Treefiddy]

Ty for the reply RCR Z!

I have actually read that thread a couple of times. My understanding has evolved in thinking my problem is extremely unique to the late model 73 240z. The end production saw the newer style 3 wire tach installed with a 'factory fix' in the ignition wiring. My solid black wire that connected the neg side of the coil to the points is spliced with another wire that appears to go back to the tach. A sensing line if you will. I have not verified this yet with a meter. I know the tach worked with the factory points/coil and this black wire has not been changed.

I can't make sense of it and other way.

Hope I'm at least kinda clear here. I've not yet hooked this black wire up to the neg side of the coil but think I will try in the morning. Unless someone explains how I'm nuts here..ha

[RCR Z]

Ty for the reply RCR Z!
I have actually read that thread a couple of times. My understanding has evolved in thinking my problem is extremely unique to the late model 73 240z. The end production saw the newer style 3 wire tach installed with a 'factory fix' in the ignition wiring. My solid black wire that connected the neg side of the coil to the points is spliced with another wire that appears to go back to the tach. A sensing line if you will. I have not verified this yet with a meter. I know the tach worked with the factory points/coil and this black wire has not been changed.
I can't make sense of it and other way.
Hope I'm at least kinda clear here. I've not yet hooked this black wire up to the neg side of the coil but think I will try in the morning. Unless someone explains how I'm nuts here..ha

You aren’t nuts, but if the Tach worked before the Pertronix install and the wire as you found them, logically to me it may not be the wires found. The Tach fix described is easy to do and put back if it does not change the issue.


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[Zed Head]

20 hours ago, Treefiddy said:

My tach no longer functions. It worked perfectly before the swap. All wiring appears to be factory with the exception on the red and black pertronix.

Does it do anything at all.  The answer might be in the fine details.  I would use a meter and check any mystery wires for power and ground before connecting them to anything.  You should at least be able to tell that connecting them won't fry anything.

[Treefiddy]

1 hour ago, Zed Head said:

Does it do anything at all.  The answer might be in the fine details.  I would use a meter and check any mystery wires for power and ground before connecting them to anything.  You should at least be able to tell that connecting them won't fry anything.

Ty man for the reply.. 

All excellent points.. I will check for voltage/ground..

It really seems like I'm one wire away. The black wire that is spliced to the black wire that connected the points and negative side of the coil. Mind you it was like this from the factory. It has to be a voltage sensing wire that drove the tach before. The black/white wires hooked to the green/white wire bypassed the inductive loop of the tach.. All factory.. only this black wire remains to drive the 3 wire tach..

I am certain I have found the 12v switched supply black/white wire and it remains on the switched side of the BR.

I'm at work ATM and can't post a drawing..but.. if you take the basic John Hull diagram for the 70-72 pertronix drawing: draw another black/white wire from the green/white wire to the pos side of the coil so it connects both to the BR and coil, then draw a black wire from the factory wire connecting points to the neg side of coil back to the tach. This is how mine was connected from the factory.. The green/white wire (which spliced a pigtail tail with 2 black/white wires) bypassed the normal inductive loop on the tach. BR still functioned and you also get 12v when key is in start. It's pretty crazy actually that there is no documentation of this. I have found 2 other post with the same situation both late model 73s..

Edit: to further clarify my situation by means of the John Hull drawing, the black/white wire shown from the tach to the positive side of the coil does not exist.. it is replaced by the black/white wire from the green/white pigtail..

Edited July 19, 2018 by Treefiddy

[Treefiddy]

Oh and to answer your question..haha

The tach did nothing at all after mods

[Zed Head]

The Pertronix ignition module acts, essentially, like a set of points.  It makes and breaks the circuit.  So you really shouldn't have to do anything special, wiring wise.  If the tach is reading the current flow, there will still be current flow.  If it's measuring voltage pulses there will still be voltage pulses.  The problems seem to be either a matter of degree/quantity or of quality.  The loop on the back of the tach is the common point for fixing the current measuring tachs.

Are you just avoiding taking the tach out?  Can't blame you.  It's a pain.  Ian at Pertronix has the answer.  RCR's link in #3.

I think that the voltage sensing tachs came out with electronic ignition in 1974.

[Treefiddy]

5 hours ago, Zed Head said:

Are you just avoiding taking the tach out?  Can't blame you.  It's a pain.  Ian at Pertronix has the answer.  RCR's link in #3.

I think that the voltage sensing tachs came out with electronic ignition in 1974.

I would like to not have to remove the tach.. haha lazy I guess!

I believe that is in fact what I have. A 74 tach in my 7/73 model. The way it was originally hooked up from the factory will not produce an inductive circuit through the tach. The harness I have at the ignition coil only has one 'true' black/white wire and it comes from the ignition switch. All other wires, with the exception of the black wire, I've identified. I will reverify this morning for voltage/ground but I'm feeling kinda confident.

[Treefiddy]

oh man.. so i hooked it up and caught my car on fire and then my house and then the neighbor's house..   naww.. kidding..

It worked!! Hooked solid black wire to neg side of coil and viola! a tach! Never even had to cut a wire.. All factory connections! re-taped wire loom and in business again! On to the heater hose/heater control valve replacement!

[Treefiddy]

 

 

 

Edited July 19, 2018 by Treefiddy