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"Houston, We Have No Ignition"
Bob Marty, via CarCraft.com: I have an electrical problem on a numbers-matching '67 RS/SS Camaro. We completed a show-quality restoration, and it all went well until it was time to start it up. The motor fired right up. However, as soon as the ignition switch was released from start to run, the motor shut down. We checked all wires and connections. With the key in the run position, our Fluke meter showed no voltage at the coil but 12 volts at the resistor wire on the firewall. As I understand, there should be an approximate four-volt drop from firewall plug to the positive side coil. Both front firewall harnesses were new reproductions. We put the original motor harness back on and had the same problem. After many "Wow, that wire is really hot" experiments, I will tell you how we got to where we are now.
First, we eliminated the yellow wire from the starter solenoid to the positive side of the coil. We then replaced the resistor wire at the firewall plug and installed solid wire from the plug to the coil. This gave us 12 volts to the coil all the time. We mistakenly thought we would just need to replace ignition points a little more often. Yeah, right-how about every 300 miles? Currently, we're running a Mallory HEI ignition module in a distributor with a high-voltage coil with 8 ohms of resistance built into the coil. We've driven the car approximately 400 miles since this, and all seems well. This ignition module is designed to run on 12 volts with this specific coil. Can you please help us understand what the heck is going on here?
We used the original coil that was OK before the restoration. Can this problem somehow be related to the ignition switch? We build nice cars, but electrical problems are not our strong points. My two sons, 8-year-old grandson, Hot Rod Tyler, and I would be grateful for any assistance you can offer us. Thanks for your help!
Jeff Smith: You have a lot of things going on here, Bob, so let's take them one at a time. A typical points system cannot operate with a full system voltage of more than 14 volts with the alternator charging. This much voltage (and the attendant current flow) will burn up the points, as you discovered. As you surmised, that's the reason for the GM resistance cable that is in the harness between the firewall plug and the coil. When you tested for voltage at the positive side of the coil with the resistance wire connected to the coil, it's likely that the points were closed. This creates a closed circuit to ground on the negative side and would produce the zero voltage reading at the coil if you were reading voltage off the negative (distributor) side of coil. The wire from the starter solenoid to the coil is a battery voltage source only when the key is in the start mode and was designed to bypass the resistor wire and feed cranking battery voltage to the coil for better starting performance. Eliminating this wire only reduces voltage to the coil during cranking if the inline resistor wire is still used to the coil.
This doesn't fully explain why the car would only run on the start mode. We've seen situations in which a car crafter has wired the ignition switch for an HEI-type distributor off the accessory side of the ignition switch. In this case, the engine will not fire until the key is released from start to run. This is the opposite of what you are experiencing. We have seen ignition switches that have melted connectors on the backside of the switch due to circuit overload because too many circuits were loaded through the hot side of the ignition switch. I would also use your ohm meter to check resistance in the resistor wire. If the reading is zero (or open), the wire is defective. This is unlikely since you have two and they both performed the same.
All factory and most aftermarket electronic ignitions are designed to run on full system voltage at ranges from 12 to 14.5 volts. It sounds like you have converted to an HEI-style distributor that uses full system voltage, which is why your ignition system is working now. This will work fine, and you should not have any more difficulties.
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