Dose anyone know the specified resistance of the calibrated resistance wire (CRW) running from the ignition switch to the coil primary on a 68 L36?

Better yet, how about the current (in amps) that should flow in the coil with the points closed? Seems Bubba had added a 1.0 ohm ballast resister to the firewall which is in series with the CRW and the coil primary to reduce the coil current. Even so the CRW is very HOT to the touch with the car not running and the ignition in the ON position. It is hot enough that I am concerned about bundling (re-wrapping) the CRW into the engine firewall wiring harness.

Last night I went to Auto Zone and got a ballast resistor for a 65 vette, 1.8 ohms but it looked awful small. It was probably a coil of NiCrome wire in a three-sided ceramic box. Connected it across the battery, the wire incandesced , cherry red and eventually I let the smoke out. Obviously it didn't work. What's the scoop?

 

I'll be following this as I was encountering the "hot to the touch" symptom myself. I found a short in both the ignition wire from the ign switch and the wire direct from the starter. After I repaired the shorts, the wires were no longer hot to the touch. I wonder if I have removed the CRW portion of the wire. I'm on the road until next week but I'll check the resistance and current when I get home.

E-mail me if you want to compare notes.

 

You can probably remove the aftermarket ballast resistor someone else installed and not have any problems if the resistor wire is ok. I'm not sure about the amps to the coil. What kind of problems are you having?

Welcome to the Corvette Forum :cheers:

 

I fergit what the amp are on closed points, but that 1.8 ohm resistor will not take being across the battery by itself...that coil primary has aninternal resistance of probably around 5 ohms....so you are drawing way ho too much power for that resistor by itself....buy another one, start the car and see if you have full system voltage at the CAR/harness end of that resistor, and about 9 volts at the coil....if so, everything is fine.....if higher than say 10 volts, you better check dwell....lower than 9 volts...same thing....
dwell is 32* as I recall, and or .017 on the points with feeler gauge....assuming altzheimers isn't set too far in....

GENE

 

Mr Vette, you were very close in what was going on, a little furhter digging and here's what I found.

The coil on a points ignition system should have an internal resistance of 1.4 to 1.8 ohms and be ballasted by 1.8 ohms. With the points closed the ignition system should draw about 4 amps (14 volts / 3.6 ohms). Half the voltage, 7 volts, dropped across the coil and half across the ballast resistor so they each should dissipate about 30 watts (7 volts squared) / 1.8 ohms. A HEI or Transistorized Ignition (TI), because of its electronic nature, does not require the coil resistance or the ballast resistor. So a TI coil has a resistance of 0.2 to 0.4 ohms. The coil in my points car measured 0.3 ohms, (either a bad coil or Bubba thought it would be neat to have a high output coil). If you do the math, my ignition current was 6.7 amps (14 volts / 2.1 ohms) and the power dissipated on the ballast resistor was 96 watts (12 volts squared/ 1.8 ohms) which is exceeding the nominal power by more than three times.

Just to test my theory, when I put a 1.8 ohm ballast resistor (from a 65 vette) in series with the TI coil across the battery, the resistor became cherry red and smoked. When I put the same resistor in series with the points coil across the battery, the resistor got warm but never hot.

In addition to finding the likely cause of the smoked wiring harness, the car starts and runs a lot better.

Just thought you might like to know.

Rick Ales