Tachometer problem after installing ignitor lll

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Joined
Jan 13, 2012
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Location
Washington
My Car
1971 Mach1, 351 Cleveland, Ram Air (not factory), C6 Automatic, AM/8 Track, Bright Red.
I found this site while googling for a possible fix...so I joined! I installed a petronix ignitor lll and a flame thrower lll yesterday on my 71 Mach1, runs great but tac now not working, also tempature gauge appears not to be working correctly, it now barely moves where it normally ran in the middle range prior to installing the Petronix. I followed the instructions that came with the parts which called for a 12V positive wire to be added to the coil from the fuse box and disconnected the resistor wire that was connected to the coil. The ignitor lll and flame thrower lll need a full 12V at all times, while the resistor wire only provided 12V at start up then cut back to approximately 8V to spare the points (as I understand it?).

Note: Yes the wire I added works with the ignition just as the resistor wire does and is off when engine is shut down.

I take it disconnecting the resistor wire from coil is the issue with my tac now not working (wiring shows resistor wire to coil came from Tac). My question is, can I reconnect the resistor wire back to the coil (positive side) in addition to the full 12V wire I ran from my fuze box...or is this going to cause issues

Any advice would be appreciate, sorry if i posted this in the wrong area...I'm a newbie.

Post2.jpg

 
I recently installed new ignition but used the MSD kit & lost the tach too, the guys here figured it for me & had to use the MSD tach adaptor as its current triggered, unsure if Petronix supply anything to fix this though.

I also had a cooler running motor according to the temp. gauge after the install but returned to near original but slightly cooler once I got the timing corrected and set

HTH

 
Thanks guys, the information has me on the right track. I did try hooking the resistor wire running from that tac back up and disconnecting the straight 12V line I installed, Tac worked but then the car wouldn't idle correctly without the full 12V line I ran, per Petronix instructions for the ignitor lll and flame thrower lll coil. What I'm wondering is if I can leave my installed 12V hooked up and also connect the old resistor wire from the Tac back up so the Tac works? I'm just afraid to try it in fear of causing damages but logic tells me the max volts would still be just a full 12V???

 
I'd suggest contacting their tech support. I've heard mixed stories on Pertronix III with the tach working or not. I've heard pertronix is suggesting adding a resistor and in some cases a capacitor. I have no personal experience with III. I've had mixed results with I and II, they are not my first choice. Chuck

 
What I'm wondering is if I can leave my installed 12V hooked up and also connect the old resistor wire from the Tac back up so the Tac works? I'm just afraid to try it in fear of causing damages but logic tells me the max volts would still be just a full 12V???
I don't think that would work. The tach is current triggered. It would likely draw from the 12v wire, and the tach would not be accurate. Hook the 12v wire just to the + module wire, hook the original coil wire to the coil +. The tach still might not be accurate because of the multiple spark feature of that ignition. If you were to try it your way, I would add a diode to the factory wire, so it wouldn't get backfed by the 12v wire.

 
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I don't think that hooking the original coil/tach lead up in addition to the new wire would hurt anything, but I agree that your tach probably wouldn't be accurate. The amount of current through the tach would drop because you have two power leads, and most of the current would go through the non resistor wire, like C9ZX has stated. I agree that a call to tech support is in order to see if they have an adaptor. I'd like to hear what you find out, because I'm thinking of installing electronic ignition as well, although my tach is now a 3 wire design.

Steve

 
[. If you were to try it your way, I would add a diode to the factory wire, so it wouldn't get backfed by the 12v wire.
Excellant ideal to protect the system. I think I'll also give Petronix a call Monday to see if they have a solution, if not I'll give a try.



I'd like to hear what you find out, because I'm thinking of installing electronic ignition as well, although my tach is now a 3 wire design.

Steve
I'll post the outcome. I've been running points on the car until yesterday and I have to admit the ignitor lll and flame thrower lll coil made a huge difference. Starts much faster both cold and warm, runs cooler, idles smoother and overall runs better. I've always been one for keeping the car old school (still have the Autolite 4300D carb on it) but decided to give in and move to electronic ignition, glad I did.

 
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Getting rid of the points is the smartest thing you could do. I like old school too but the points are just too old school. They burn out, they go out of adjustment easy, they are a pain to set up and they really don't do well at high RPM's. :)

The older fords (ours included) had a weird tach setup. It's not conventional so normal instructions on how to make it work do not apply. I can't tell you how to fix it but trail and error is not going to be a good strategy. You should find out for sure what to do or you might ruin a good tach.

 
Not sure if this will help but my 1800S Volvo sports car has a complete new Electronic Mallory Distributor put in by the p/o so the car would have electronic ignition.

The car is a 4cyl however the distr is made for both a Volvo 4 cyl and Ford 8cyl with only a change in rotor type to switch between the 2 motors.

His replacement had the car working fine but the Tach did not work as he connected a line directly to the coil from the unit so it did not pass through the tach.

I took the 2 original tack wires and connected one to the unit and the other to the coil so the current could pass through the tach wire loop.

After doing this connection the tach worked fine.

Only a thought and I hope it helps..

AJ

 
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You can run a key switched 12v wire directly to the red wire on the Pertronix (don't connect to coil) and leave the stock resistance wire connected to the coil. This will give you the full 12 volts to the Pertronix but limit the voltage to the coil. Don't bypass the pink resistor wire between the tach and the coil, running a full 12v through the tach will fry the isolation transformer in the tach, that supplies the pulsed signal to the tach electronics.

 
You can run a key switched 12v wire directly to the red wire on the Pertronix (don't connect to coil) and leave the stock resistance wire connected to the coil. This will give you the full 12 volts to the Pertronix but limit the voltage to the coil. Don't bypass the pink resistor wire between the tach and the coil, running a full 12v through the tach will fry the isolation transformer in the tach, that supplies the pulsed signal to the tach electronics.
Thanks Don, now that's thinking outside the box, I just assumed the 12V "had" to be ran through the coil to the ignitor. My only issue is that I also added a flame thrower lll coil which calls for a full 12V (according to the instructions that came with it). Knowing that running a full 12V through the tack would fry it is priceless information, glad I held off trying that. I'll be talking to Petronix tomorrow and ask if your suggestion might work (I suspect they may call for a full 12V to the Flame Thrower since it's then connected to the igniter lll).

coil.jpg

 
You can run a key switched 12v wire directly to the red wire on the Pertronix (don't connect to coil) and leave the stock resistance wire connected to the coil. This will give you the full 12 volts to the Pertronix but limit the voltage to the coil. Don't bypass the pink resistor wire between the tach and the coil, running a full 12v through the tach will fry the isolation transformer in the tach, that supplies the pulsed signal to the tach electronics.
Thanks Don, now that's thinking outside the box, I just assumed the 12V "had" to be ran through the coil to the ignitor. My only issue is that I also added a flame thrower lll coil which calls for a full 12V (according to the instructions that came with it). Knowing that running a full 12V through the tack would fry it is priceless information, glad I held off trying that. I'll be talking to Petronix tomorrow and ask if your suggestion might work (I suspect they may call for a full 12V to the Flame Thrower since it's then connected to the igniter lll).
I believe you would need a Flamethrower coil with 1.5 ohms resistance to work with the stock resistance wiring (Flamethrower III has 0.32 ohms). Let us know what Pertronix tells you. know that it is also possible to have your tach rewired by a tach repair shop to work off the negative coil connection, like most aftermarket tachs.

 
The petronix III will not work with the factory tach. The signal the PIII generates cannot be read by the OEM tach.

The PIII uses a Square wave signal that a modern tach uses which is digital uses to show RPM. The original ford tach uses a analog wave.

You might be able to use a MSD tach adapter that turns a digitial signal into a analog signal but i've heard the oem tach may not be accurate after.

The PII and PI are compatible with the OEM ford tach

 
Well I talked to a Petronix Tech, they are painfully aware of the issues the ignitor lll causes with older Ford analog tach's and do not recommend using the ignitor lll on cars like my Mach 1 (if I still want to use my old tach). You would think they would advise people of that.

He recommended I try running my installed 12V line directly to the ignitor and connect my resistor wire from the tach to the flame thrower lll coil. He explained the ignitor needs the full 12V but the flame thrower coil will operate fine with the reduced volts through the resistor wire. He caution the tach "probably" wouldn't be completely accurate but should operate. I asked about using the tach adapter from MSD and he advised it wouldn't work with the ignitor and they presently don't have an adapter that will work with it.

His other recommendation, "if I have to to have my old tach and it has to be accurate" was to try an ignitor ll wired as above.

Bottom line, don't install an ignitor lll if you're using your old tach on your 71 Mustang and you insist on it being accurate.

Thanks for all the great feedback, you guys were spot on. I'll probably try the recommended rewiring later today and let you guys know what happens.

Jim

 
know that it is also possible to have your tach rewired by a tach repair shop to work off the negative coil connection, like most aftermarket tachs.
http://www.rccinnovations.com/Mustangs.php

I almost went that route since I put MSD on my car. I decided to use the tach adaptor for now. My tach seems to be within 200 RPM with the adaptor. If it dies, I will just have it converted.

 
You can run a key switched 12v wire directly to the red wire on the Pertronix (don't connect to coil) and leave the stock resistance wire connected to the coil. This will give you the full 12 volts to the Pertronix but limit the voltage to the coil. Don't bypass the pink resistor wire between the tach and the coil, running a full 12v through the tach will fry the isolation transformer in the tach, that supplies the pulsed signal to the tach electronics.
Thanks Don, now that's thinking outside the box, I just assumed the 12V "had" to be ran through the coil to the ignitor. My only issue is that I also added a flame thrower lll coil which calls for a full 12V (according to the instructions that came with it). Knowing that running a full 12V through the tack would fry it is priceless information, glad I held off trying that. I'll be talking to Petronix tomorrow and ask if your suggestion might work (I suspect they may call for a full 12V to the Flame Thrower since it's then connected to the igniter lll).
I believe you would need a Flamethrower coil with 1.5 ohms resistance to work with the stock resistance wiring (Flamethrower III has 0.32 ohms). Let us know what Pertronix tells you. know that it is also possible to have your tach rewired by a tach repair shop to work off the negative coil connection, like most aftermarket tachs.
I connected the resistance wire to the Flamethrower III coil and ran the full time 12V wire to the Iginiter III, the tach now works (accurate ?) and the car seems to be running fine.

 
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