Does resistance at the distributor cap center contact matter?

[Old Henry]

I got a new distributor cap for my 47 V8 and got all of the wires installed and checked continuity between the distributor terminals and the end of the wires. All is well except the center coil wire terminal. There is complete continuity to the outer ring of that terminal but the center rounded part has about 30 ohms resistance. The new cap I just took off has the same. The old cap that new one replaced had no resistance. I checked two other old caps. One had resistance and the other didn't. The center contact has the appearance of brass around the edge with a black domed insert that has the appearance of carbon. See photo. There is no resistance from the wire end to that brass part but 30 ohms resistance at the "carbon" center.

Is resistance of that center contact point OK or should I keep buying new caps until I get one without any resistance?

[petehoovie]

Originally Posted by Old Henry

I got a new distributor cap for my 47 V8 and got all of the wires installed and checked continuity between the distributor terminals and the end of the wires. All is well except the center coil wire terminal. There is complete continuity to the outer ring of that terminal but the center rounded part has about 30 ohms resistance. The new cap I just took off has the same. The old cap that new one replaced had no resistance. I checked two other old caps. One had resistance and the other didn't. The center contact has the appearance of brass around the edge with a black domed insert that has the appearance of carbon. See photo. There is no resistance from the wire end to that brass part but 30 ohms resistance at the "carbon" center.

Is resistance of that center contact point OK or should I keep buying new caps until I get one without any resistance?

[Terry,OH]

Carbon, when compressed is conductive. There should be resistance between the center carbon brush and the coil wire terminal. The resistance is most likely much less than your measuring. So yes the resistance does matter. A cap without resistance, in the center brush, will have a hard time conducting the high voltage to the rotor. This is true of the early Ford complete ignition system, points, plug wires, coil HV wire, cap terminals.

[Jack E/NJ]

>> A cap without resistance, in the center brush, will have a hard time conducting the high voltage to the rotor.>>>


A cap without resistance usually means zero ohms. Zero ohm conductor seems like it should have an easy time conducting.


Anyway, 30 ohms is insignificant for the high voltage pickup. The new cap seems fine.

[Ggmac]

If the reading is from the ignition wire to the center carbon , you should be good . If you could read the resistance between the brass encircling the center carbon , both from the inside of the cap , I’m pretty sure it’ll be much less resistance.

[Old Henry]

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Thanks for all of your help. The ohm reading was the same between the end of the wire and the center distributor terminal as it was between the brass that that center terminal fits into and the terminal itself.

I went ahead and installed the wire loom and everything else. The new cap did not help my problem. See this thread for the continuing saga: https://www.fordbarn.com/forum/showthread.php?t=332254