Repro tach + Pertronix == Help!

[davepl]

My reproduction tach reads 0 with the key off.
With key on but engine NOT yet running, it reads 2150.
It reads 4800 with it running (likely around 1200).

I have the Pertronix Igniter III module in stock-looking distributor. No HEI, but its likely a similar problem.

My DVM shows 12.3 volts (engine off) at BOTH sides of the coil. I have the red wire from the ignition module in the distributor going to the + of the coil and the black to the -, and the pickup from the tach going to the neg (-) post on the coil. They're embossed so hard to get backwards, and it runs.

I've read a ton of HEI-Tach searches without much success. Sounds like a member called Necromancer can recalibrate the old tachs. People talk about a filter circuit, some argue that's only for radio interference, and so on. The catalogs for these all say "Not for use with HEI", but they just work for some people it seems. But not for me.

Most of those threads are up to 9 years old, so I have to ask:

Can someone tell me what the current state of the art is for running a reproduction tach with an updated ignition?

How can I make it work?

Many thanks,
Dave

['68OrangeSunshine]

Does the tach have a 6-Cyl / 8 Cyl switch in the back?
I have a Pertronix Ignitor II and an Auto Gage tach, I have no problems with it on a 292 L6. It worked good when I had points, too.

[davepl]

No, not switch that I can tell. But even if it were a 6 cyl tach I don't get why it would read > 0 with the key on and engine off. That's just showing it 12V.

It really sounds defective, but given sometimes some magic is required, I'm looking for the magic...

['68OrangeSunshine]

Could be a bad Tach unit. I dunno. Maybe there's some wierd mojo in the Pert/III gizmo which, as I understand is a multi-spark unit like a mini-MSD. Could that be where your tiny demons lie?
Does the Tach work normal on another vehicle system? [W/o P-III]
Have you querried Pertroinix Tech Support?

[davepl]

The multi-spark thing is a pretty cool theory, I wonder. It's a long weekend so no retail support, I'll have to wait.

From the Ford forums (of all things) someone said the Ignitor I and Ignitor II work with the (Ford) factory tachs but that the Ignitor III does not. That guy contacted Pertronix tech support and was told to run an Ignitor II was well. Odd advice: use our old product.

Also, I have my distributor (actually the Ignitor III module) connected directly to the (+) and (-) of the coil. It's probably more about resistance wires, but some show the module powered from the fusebox, but it really should be the same deal.

My DVM has a Hz feature on it, I wonder if that'll tell me anything?

['68OrangeSunshine]

Have you bypassed the resistance wire? It's a 20 white/purple/orange line out of the bulkhead connector terminal block. In stock mode it splices into two 20 Yellow lines -- one to the starter, other to the coil.
For high energy ignition [GM and aftermarket] you will want a 10 or 12 ga. wire from Ignition Unfused on the firewall fuseblock directly to the Pos [+] coil terminal.
Sound like your module connections to the coil are right. Coil [-] Neg is normal Tach pickup.
Funny that the Pertronix tech would tell a guy on the Ford forum to retrofit to a P/II. Might be all about multi-spark demons. I was thinking of the P/III for a future project, but being tach-blind is a deal killer.
By the way, who makes the Repro Tach and where?

Your call, but maybe you might want to ask a Moderator to move this thread over to the Electrical Forum.

[davepl]

No objection on moving it to electrical, though I'm not sure who to ask.

My biggest demon is the fact that it reads 2150 when the engine isn't running as soon as you give it 12V. I hooked up my DVM in Hz mode and couldn't find a signal. Is this finally the excuse I've been waiting for to buy a scope? Probably not....

[67 cst swb]

Pertronix 909-599-5955

[ic1480]

Any luck with the Petronix III. Same set up here. thanks

[davepl]

Just to wrap up my thread on this, I borrowed a different reproduction tach from a friend, it worked, so I bought that from him and sat the one described here aside.

I think the multispark feature might still be causing it to read high, but at least it works mostly!