74' No Start Troubleshooting Help Needed

[Robert S.]

Re: 74' No Start Troubleshooting Help Needed

I will try that approach the next time it won't start. When I changed out the starter solenoid last year all the wiring looked to be in excellent condition and I was ultra careful to mark each wire so I got it back on the right solenoid terminal but I suppose the wire itself could have an intermittent somewhere in it's path to the coil. After all the wiring is now 40 yrs old.

[Michael W.]

Re: 74' No Start Troubleshooting Help Needed

Measure the voltage across the points when the car is running. Should be at some value considerably less than battery.

[Robert S.]

Re: 74' No Start Troubleshooting Help Needed

I can and will do that. Here is my dilemma. If the car is running then the points are being fed via the resistance wire. I can only imagine two conditions for the resistance wire, either it works as intended or it is broken. If it works as intended then the voltage to the points should be as GM intended. If the wire is broken the car would not run once the ignition switch is released from start to run.

[Michael W.]

Re: 74' No Start Troubleshooting Help Needed

Or the points are still being fed 12V or higher due to a wiring error.

[Robert S.]

Re: 74' No Start Troubleshooting Help Needed

With the engine running at idle, using a VOM, I measured about 7.8V DC at the minus side of the coil (wire going to the points).

[Michael W.]

Re: 74' No Start Troubleshooting Help Needed

That sound about right. No idea why the points have such short life.

[Richard M.]

Re: 74' No Start Troubleshooting Help Needed

Coming in late but I've been lurking on this one throughout the troubleshooting exercise.....

As far as points burning up, as Michael and others mentioned, during crank is when the coil+ sees full battery. This is via the Yellow wire at coil+ connected to the Solenoid R terminal, which only gets Bat+ during crank..

I would check the Yellow wire in the harness at the Solenoid R terminal, to be sure it is not chafed and occasionally rubbing on the Solenoid BAT+ main lead or internally in the harness to main power to the electrical system. After the engine heats up it may be shorting to BAT+, yielding 12v+ at the coil+, possibly burning points due to high coil voltage.

Also, the Purple Solenoid wire in this harness can become compromised over the years due to long crank times. This sometimes melts insulation on other wires in the harness and is exacerbated at high engine bay temperatures. Example pic below from a '66 engine harness with that condition.

Rich

[Robert S.]

Re: 74' No Start Troubleshooting Help Needed

Thanks - I had not considered chafing of the yellow wire and can see it is a possible explanation for my points burning issue.