| Esteban34 | -- 10-30-2012 @ 9:52 PM |
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Dear Group, I have burned out two under-dash resisters on my 34 Ford Tudor. Any idea what causes them to blow? -- esteban adonde vas, estas alli Esteban
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| ford38v8 | -- 10-30-2012 @ 10:44 PM |
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Estaban, To begin an explanation, it may be helpful to review the function of the resistor: The coil wants a steady supply of voltage of between 3 1/2 to 4 Volts, and the function of the resistor is to smooth out the varying voltage from the charging system, lowering the voltage to the required value. The early Ford resistors are made for a 6V system. A higher voltage will overload the resistor, shortening it's life. Assuming you are not running an 8V or 12V system, I would suspect a direct short to be the cause. Remove the connection at the coil, as the coil itself will show a closed circuit if left connected. You may have a partial or intermittent ground, which might be detected by wiggling or moving the wire about. The fault may be anywhere in the circuit from the coil back to the connection at the resistor itself. Alan
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| 40 Coupe | -- 10-31-2012 @ 4:24 AM |
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I agree with Alan. There should be only ONE wire on the resistor that goes to the coil and only the one wire at the coil and that wire has to have it's electrical insulation in good order. It may be best to replace the wire with a new wire and if there are any other wires in this part of the ignition circuit either at the resistor end or the coil end, they are not in the proper location. The resistor when operating properly will get very hot, too hot to touch with your hand. The heat does place a lot of stress on the resistor but few fail when everything else is correct.
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| Esteban34 | -- 10-31-2012 @ 7:13 PM |
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I may be misdiagnosing the problem. I looked more closely at the resister. It has what looks like burn marks on the brass screw heads that attach the resister to the resister block. I did not know the resister got that hot. Maybe the heat just made the marks and the resister is still good. Is there a test for the resister? adonde vas, estas alli Esteban
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| ford38v8 | -- 10-31-2012 @ 8:28 PM |
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Estaban, If the engine runs, your resistor is good. Alan
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| Old Henry | -- 10-31-2012 @ 10:39 PM |
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You can test it with an Ohm meter. Should be 40 Ohms or thereabouts. See here: http://macsautoparts.com/early-v8-ford-mercury-ignition-coil-resistor-40-ohm-replacement-style-ford-18-12250/camid/F30/cp/JS0R3CHL1074133/ If you don't care about the exact reading, what ford38v8 said is good enough. The car won't run at all if the resistor is burned out. If it runs, it's not burned out. Old Henry (The older I get, the better old looks.) This message was edited by Old Henry on 10-31-12 @ 10:45 PM
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| trjford8 | -- 11-01-2012 @ 7:32 AM |
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Resistors do get hot. If you put in a new one and it smelled like it was burning that is not unusual. They get hot and burn off some of the coating on the wire coil. Like others have said if it still runs it is still good.
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