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Old 04-07-2021, 10:35 AM
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edwardc edwardc is offline
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Quote:
Originally Posted by Golfdad75 View Post
My ignition switch drives me crazy. Sometimes it just doesn't work. I can go down below and flip the battery switch and it seems to work. I have replaced the battery switch and nothing changed. If It takes awhile starting and I try again it will act as there is no connection. If I wait a couple of minutes it may work or I may have to switch the battery switch. It always works but keep wondering when it is not going to. . Yes I have replaced the ignition switch also. Any thoughts or insights.
There is another possibility.

I used to observe this exact type of behavior in my old Volkswagens. The problem turned out to be in the starter. The explanation is a bit long, so bear with me:

The solenoid actually consists of two windings. This is done because it takes more power to get the solenoid to engage than it does to hold it engaged, so both get energized when the start button/key is activated, and only one stays energized once the solenoid pulls in. One of the windings is connected between the solenoid terminal and ground. This one that is energized as long start button/key is activated. The other winding is connected between the solenoid terminal and the positive terminal of the motor (NOT the battery positive terminal!!!). The result of this is that the second winding gets energized too by sinking its current through the motor to ground. This provides the extra pull to get the solenoid to engage. Once the solenoid engages, it applies +12V to the positive motor terminal to crank it. This also causes both ends of the second solenoid winding to now be at +12V so current stops flowing through it. Its a clever design.

The problem comes in when the starter ages a little, and the resistance through one or more of the brushes goes up a little. Its not enough to affect the starter, but it reduces the current through the second winding. Combine that with voltage drop in the wiring, temperature, and the exact state of charge of the battery, and sooner or later its just past the threshold where the solenoid doesn't pull in. Wait a few minutes, perturb the starter, or let the temperature change, and it works again.

The "Correct" fix is to get the starter rebuilt, but this isn't always possible or practical.

On the Volkswagens, my workaround was to momentarily bridge the battery + terminal to the solenoid terminal with a screwdriver. This bypassed all the wiring drop, and gave just enough extra juice to pull in the solenoid and "bump" the starter. Once it was moved to a new spot, it always started fine.

My long-term fix was to install a relay close to the starter, using the start wire to drive it, and using it to energize the solenoid terminal. With its short run of wire, the voltage drops were minimal, and this proved to be a reliable fix.
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1977 Pearson P-323 "Dolce Vita"
with rebuilt Atomic-4

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