I recently found out (http://forums.corvetteforum.com/c3-t...utor-coil.html) that the ballast resistor on my '69 is not origional. The car origionally had a factory tranistorized ignition--I found the disconnected modual--and was converted back to a points ignition. This was probably when the resistor was added.
The car does run well, but I wonder if the ignition resistance is correct, and if I'm getting the correct voltage to the coil.
Does anyone know the correct values?

 

The GM wiring diagram I have for the TI shows a resistor in the white wire 12 from the ignition switch. Actually, it shows 2 resistors- one from the switch and the other one at the + side of the coil.
What the actual resistance is not shown on the print. No surprise there.
TI Specialties might know.

 

Distributors are are a hobby of mine, maybe I can help.

While the engine is cranking the coil should be receiving 12v on the Pos side of the coil, once started the the Pos side of the coil should be receiving 9.5v

If your car is started and running, with a points distributor you'll have approx 9.5 volts on the Pos side of the coil terminal. This could be as low as 8.0 volts all the way up to 10v depending on the resistive value of the porcelain resistor mounted on the firewall or the resistor wire, being used that might/maybe, be in the wiring harness loom.

There is another part of this Start System that comes into play here. When you attempt to first start the car with the key switch in the crank position there is another wire from the outside post on your starter solenoid the "R" terminal that becomes energized, providing a full 12v to the Pos side of the coil to make initial startup much easier. Once you release the key to the run position and your car is running the R terminal becomes disconnected and the wire from the ballasts resistor or ballistic wire now takes over. This then limits the voltage to the approx 9.5 volts. The reason the voltage is knocked down from 12v to the 9.5v bracket is once the car is running, the coil will still put out it's max voltage at 9.5v via the resistor wire or ballast resistor. The points simply last longer before they have to be replace, running on 9.5v vs 12v. The truth be known, if this is a warm weather car and basically a stock engine it will start just fine on the 9.5v.
If you wanna send me a Pm I'll give you my phone number and we can go into more detail.

The "R" terminal on your starter solenoid, equals/stands for; relay, not resistor as some think.

Regards

 

Hey, Tim, good to hear from you. I'm hopeing for another Bird run soon. Do you or did you have a ballast resistor on your fire wall, or a resistance wire as mesntioned in the reference thread?
Anderson, thanks for the reply. I more or less remember the theory. Now that you refreshed my memory, I'll check the voltages and go from there.

 

Great;..... take care...... If I can help gimme a shout.
Regards

 

The resistor wire is built into the harness somewhere- or maybe it's the whole length of the wire.

Actually I'm in Victorville right now. I'll be here until the 27th then to the east coast. I'm ready for another Bird run too- But Ol' Red is in the middle of a major rebuild. I've already gone thru the trans, engine is on the stand, and I'm building another rear end and 3" half shafts too. After that, I'm going to put an original style tach and speedo back in, and figure out how to get the lights in the rest of the gauges to be bright enough I won't need a flashlight. Probably LED's in them. And then a new top. It just never ends..

 

If the original 'built-in' resistor wire is still in the system (entire wire from fuse block to coil is resistance wire for the factory build), it is probably the wrong value for a points coil. The resistance of that wire was different for points ignition (1.77-2.05 ohms) or TI ignition (41-.51 ohms).

For a points ignition, that ballast resistance (whether from wire, discrete resistor, or both) needs to be appropriate for whatever coil you are running. That resistor is not [specifically] there to lower voltage; it's there to limit current to the coil so that the points don't fry.

My recommendation is to measure the resistance value of the resistance wire, AND that of the added resistor, to determine what total resistance is in that circuit. Then, adjust the resistance in that ignition line to match with a stock points coil and make sure that the coil you have is correct for points ignition. That should get you back to a stock points ignition setup.

I'm guessing that the added resistor was placed there to make up for the difference in resistance needed when it was changed over to a points-type system.

 

I have TI on my 68 that has been "modified" over the years. Should it have the feature described above that delivers 12V to the coil when the engine is cranking? I have not seen a wiring diagram that shows the TI system with enough detail that I could understand.
Will

 

If I'm reading the schematic in the Chevrolet Chassis Service Manual correctly (Sect. 6-Y, Breakerless System, Fig. 3i), there is a wire from the starter solenoid going to that system; but, it does not go directly to the coil. It feeds into the engine harness and/or the TI harness.

 

From the GM Service info I have
I agree with 7T1- it appears to me that feeding 12v during cranking to the + side of the pickup coil would provide a stronger signal to the amplifier.

 

Thanks for the responses and drawing, that is how mine is set up, the wire from the solenoid was not connected so I was not sure. When the engine is running there is only 3.0 volts +/- on the positive side of the coil. Is this normal or should it have 8-10 volts as described above for the points ignition system?
Will

 

I have no idea what the voltages should be for a TI ignition. And, unless you have a very good voltmeter with a very high input impedence, you shouldn't be delving into electronic circuitry. If you have the right equipment, have good documentation on the device, and know what you are doing, that would be fine.

You need the detailed info on your car that is found in the Chevy Service Manual for your year. It will detail the hook-up of the TI system and probably show how to check it out. Otherwise, dig around on the internet for the info you need to set it up and check it out....BEFORE you go "testing" it out.