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Old 09-01-2022, 09:26 AM   #1
CatMan1
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Default Bad Ignition Switch?

I am suspecting that I might have a bad ignition switch. It came with the car and doesn't look too old so it's a reproduction. I noticed that the magneto quit one day. I've had the post out and it looked clean and had continuity through it. The wires appear to be routed correctly. Last night I noticed that with everything off and the battery disconnected I got continuity from the 'MAG' to the 'DIM', 'BRIGHT' and 'TAIL'. This is on the back of the switch with everything off. I would not think that is correct, right? I'm thinking this would de-magnetize the magneto? This afternoon I'm going to hook up the battery and see if I have voltage down to the post......which would be wrong. Also, I did make a test light to connect to the magneto post to test it. No light. I'm more concerned about the switch at the moment. Also wondering if it would have any effect on the car not charging.
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Old 09-01-2022, 11:37 AM   #2
rotorwrench
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Default Re: Bad Ignition Switch?

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I performed magnaflux inspections for a number of years and demagnitised parts afterward using an AC coil. Permanent magnets will lose gauss after a time but some residual remains for many years. With the type of magnets a model T has, they should remain with good enough gauss levels to last at least a decade or two.

The 1919 through 1927 model T, had a power wire that connect from the battery to the switch. A circuit won't flow current till it has a pathway back to the ground source. There may be a problem with the switch but it could be checked with an Ohm meter for continuity to ground. A test light can be used but it has to be isolated and then power applied to one side to safely use the test light on the other side. The magneto was used to power headlights in some early model T cars but they used a high voltage bulb to do that. A regular bulb would likely burn out. The Mag terminal on the switch is either open or it's connected to the coil box to function the trembler coils. The switch should be tested independently after isolating each terminal that is applicable to it's respective circuit. Light circuits should not be involved with magneto function. When the switch is on battery, it has a common connection with anything else that works off the battery. Look at a photo of a switch repair kit and you can see that ignition circuits have a separate contactor on the rotating plate.
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