Re: Intermittent Starting Issues

Posted by DavidPackard On 2022/9/2 0:16:38
I would stop, disconnect the battery and drag-out the multi-meter. Your symptoms suggest something is failing . . . or a short as Ross said. There is a possibility of several difficulties, the puff of smoke, the loss of battery voltage when the headlights are ON, and finally the starter switch. Before anything is powered again a lot of circuits have to be checked. However, assuming the car was OK in the Spring, unless the wiring was worked on during the Summer the probability of something being mis-wired is low.

The puff of smoke could be a short in the ignition switch, or corrosion between the power feed and the GA circuit . . . that would go a long way to explaining the other symptoms. The loss of voltage when the headlight switch is cycled could be the toe switch, but I would let the multi-meter tell me if it's bad. They frequently fail abruptly. A short in 15-WGX, &-BR, or 8-G are possibilities. Keep reading, because I don’t think a short in the head light circuit would make the engine shut-off. Checking the headlight circuit may prove to be a lower priority task.

I’m hung-up on why when the headlights were turned on there was insufficient power/voltage to run the ignition. The circuit starts at the battery, down to the starter, back to the ammeter (1-R), through the ammeter to 2 –RY, and finally 21B-R2W to the ignition switch. Remember that’s exactly the circuit that powers the ignition when the starter motor is engaged (hundreds of amp of draw). I’m not convinced a simple short in the headlight circuit could defeat the ignition . . . given a few minutes before the starter draw didn’t defeat the ignition. I’m thinking you would smell something if the current got that high in the headlight circuit.

I agree with HH56, an intermittent OPEN in the ammeter could cause the problem. In this scenario you’re running on either the battery or the generator. The generator voltage is enough to close the reverse current relay, but the capacity of the generator is low because of low engine speed. If the highlights are turned ON (large deflection of the ammeter into the discharge side) and then the ammeter OPENs . . . game over the 16-20 amps of headlight load exceeds the generator and the voltage take a nosedive (remember you’re disconnected from the battery). The same nosedive would occur if the reverse current relay is open. In this scenario the failure was modeled as an OPEN in the ammeter, but any continuity loss between the battery and ignition switch terminal ‘GA’ would do. I’ve seen battery cables corrode between the copper cable and the connector that attaches to the battery post. Loose or corroded connections fall into the same category, as does the ground strap to the battery.

An intermittent OPEN in the 1-R, 2-RY, 21B-R2W circuit, or an intermittent in the positive cable to the battery would explain a lot of the symptoms . . . that’s where I would start.

Let’s return to the headlight circuit and the introduction of a short circuit. Again, at a very low engine speed (generator ‘off-line’), the normal load of 16-20 amps in the headlight circuit does not defeat the ignition, so the headlight load would have to be high enough to produce a voltage drop of something in the order of 2 + volts in the 1-R, 2-RY circuit. The built-in headlight circuit breaker would not open in time to protect the ignition voltage from falling below the threshold needed to provide spark. In my opinion you would smell something amiss with that amount of over-current.

Dumb question: You said you changed the battery, is the polarity correct? That could be another kettle of fish to fry.

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