| LarryK | -- 09-08-2013 @ 5:44 AM |
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What is the ohm rating of the ignition resistor 18-12250? Thanks
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| 40 Coupe | -- 09-09-2013 @ 4:14 AM |
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It is approximately 0.5 ohms, your going to need a digital ohmmeter and clean the two terminals before reading.
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| supereal | -- 09-09-2013 @ 2:54 PM |
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It should also be pointed out that the element of the resistor is a piece of nichrome wire, such as was used in toasters. As the system voltage increases, due to higher engine revs, the resistor heats up. This increases the resistance, in effect limiting the voltage, due to the heating of the wire. Thus, the resistance of the unit will vary considerably as the vehicle is driven. This message was edited by supereal on 9-9-13 @ 2:56 PM
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| LarryK | -- 09-11-2013 @ 5:38 AM |
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Thanks 40 Coupe and supereal. I measured 0.4 ohms. MAC's catalog gives 40 ohms. I didn't think that could possible be right. Using the temperature coefficient of resistance for nickel, I calculated approximately 50% increase from 70F to 200F. Not sure what temperature is reached during operation, but it must be substantial given the ceramic core. This all seems to be in line with the primary ignition circuit total resistance of 1.0 to 1.33 ohms given in the Service Bulletin specifications.
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| supereal | -- 09-11-2013 @ 11:08 AM |
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The slotted cover over the resistor prevents most of us (not all) from branding a finger by touching it. It doesn't get red hot, but close to it. The usual problem, (particularly with the foreign repros)is that the constant expansion and contraction of the element tends to loosen the terminals at the ends. Otherwise. the resistor is reliable.
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