Topic: Tachometer Failure

[jwc66k]

There is another area of potential failure, the pivot points of the needle. After 50 years, they could get gummed up, or wear to the point of not allowing the needle to move. A similar pivot problem occurs in the clock. I took apart several Rally Pac clocks to see what their problems were (mostly the contacts "arced" together) so I guess it's time to take apart the tach side.
Jim

[69cobrajetrugae2]

Thank you Randy and Jim!

Randy, from a previous post you mentioned that with respect to a tach car, at the ignition pigtail the red/black or a black/red wire is the 12V supply to the tach which I assume plugs in at the tach.  Next if I recall correctly, the pink resistor wire plugs in after the tach then loops around as you mentioned and terminates at the firewall mated with the 12V starter relay bypass wire.

I believe there is a connector halfway down the intake manifold.  I am still not 100% clear about what the engine harness looks like in factory form.  One can order from NPD and other retailers a ignition switch pigtail with and without a resistor wire.  The pigtail with the resistor wire is for non tach cars I will assume since it's coiled up and has considerable length.  What parts would I order to restore a tach car wiring that's been cut spliced and altered to accept a petronic ignition and a fellow desires to reverse the damage and revert back to factory form?

I assume it would be plug and play since cutting a resistor wire is expressly forbidden.  This is giving me a headache and I'm likely not the only one but getting it right is important since stalling the engine and getting stranded is the expected outcome if something is missed.

[midlife]

Thank you Randy and Jim!

Randy, from a previous post you mentioned that with respect to a tach car, at the ignition pigtail the red/black or a black/red wire is the 12V supply to the tach which I assume plugs in at the tach.  Next if I recall correctly, the pink resistor wire plugs in after the tach then loops around as you mentioned and terminates at the firewall mated with the 12V starter relay bypass wire.

I believe there is a connector halfway down the intake manifold.  I am still not 100% clear about what the engine harness looks like in factory form.  One can order from NPD and other retailers a ignition switch pigtail with and without a resistor wire.  The pigtail with the resistor wire is for non tach cars I will assume since it's coiled up and has considerable length.  What parts would I order to restore a tach car wiring that's been cut spliced and altered to accept a petronic ignition and a fellow desires to reverse the damage and revert back to factory form?

I assume it would be plug and play since cutting a resistor wire is expressly forbidden.  This is giving me a headache and I'm likely not the only one but getting it right is important since stalling the engine and getting stranded is the expected outcome if something is missed.

Every car has a pink resistor wire, and it never extends past the firewall plug.  What NPD sells is not a factory replacement, as the original has only one male bullet and the other end of the resistor wire is embedded in a molded plug.  NPD's version has two male bullets. 

As for an engine gauge feed harness with a mid-way connector, I do not know of that, although there is a plug for the oil pressure extension line; that's it.

You can cut the pink resistor wire and butt-splice it (mechanically); you simply cannot solder it as most people would like to. 

For your repairs, add up the resistance of what pink resistor wire you have left, and see if it gets close to 1.3 to 1.7 ohms.  If it is short of that, you'll need to add length of it until it does.  Simply butt-splice it (cover with shrink wrap) and tape it up within the harness (or leave it free-floating).

Best solution, of course, would be to send it to me and let me fix everything...

[69cobrajetrugae2]

Randy, here is a thread on the subject.  http://fyi.boardhost.com/viewtopic.php?id=1382

 It seems to me that little is changed resistor wire in the circuit wise, from 64 to 69.  Is my assumption correct?

When my tach went out I called this company for repair information. http://speedocheckca.com/instrument-clusters/4648424

 Mike the owner quoted me 200 and the better part of a week for the turn around so I dropped it off.  The next day he called and said it was ready and that the bill was 90.  I believe the horseshoe failed instead of the usual fried guts. A horseshoe is instrument repair lingo for the transformer since it resembles a horseshoe.

 I'm beginning to suspect that an over voltage event fries the tach.  Jump starting another car or the voltage regulator is bad or the battery is soft shorting for example.

Mike said that he thinks it's safe on the tach to sample the current flow in the primary circuit and that we have 6 volt coils.  I studied conventional ignition system design and it's a evolved electrical engineering art form.  The coil does the work and ford yellow tops are the best.  After my friend re-curved my distributor we spun it up on his machine and at 6000 RPM crank the radar looking blips lined up perfectly.

"If I bought the best aftermarket distributor available would I gain an improvement, performance wise?" I asked him.

 "No, you can see that yours is doing the job as good as it can be done.  If you get into 12 to 1 compression you may need a hotter spark so in that event you may need to upgrade" he said.

The condenser is in series with the points as we know.  When the points break collapsing the primary coil flux field the condenser sets up a different flux field of some type, there are numerous opinions on which type of field it is, which wrings out all the voltage out of the primary side of the coil to the secondary side for a hotter spark.  The polarity of the collapsing primary coil field can be observed on the points since there is a hole on one point face and a mound on the other point face, we have all see that.  Points with a hole in the center of both point faces is a evolved design for increased longevity.  The violent point break is part of the hot spark discharge at higher RPM duty which is one reason petronics is not worthwhile in my opinion.

 Don't invite me over to your house to shoot the breeze with open mustang hoods if you have a petronic system because when you go inside the house to get more beers it will be in the trash when you come back, I can't help it.

I have a GM resistor wire in the green asbestos jacket and I'll run some tests on it under the load of a auxiliary radiator fan and report what I find as well as the current flow of the positive side of the coil on my mustang.  Thanks Randy and the rest of you guys!

[Brian Conway]

[quote author=midlife
Every car has a pink resistor wire, and it never extends past the firewall plug.  What NPD sells is not a factory replacement, as the original has only one male bullet and the other end of the resistor wire is embedded in a molded plug.  NPD's version has two male bullets. 

FWIW;  The NPD resistor wire.  When I was wrestling with my broken tach I got this wire just in case.  Turns out it is pretty much useless.  I abandoned the Rally Pack and jumpered the ' PINK ' resistor wire male bullet to the ' BLACK ' female connector and called it good.  Brian

[69cobrajetrugae2]

Did you get your rally pac repaired Brian?