[Healeys] Distributor to spark plug lead continuity

John Harper ah100register at gmail.com
Thu May 21 10:10:51 MDT 2020


Lin

To reduce interference as we had in the 1950s, resistance was added in the
plug leads. Early televisions that were 405 lines and received on a lower
frequency than today; interference was so bad that a taxi idling outside
the house was enough to totally break up a picture. People who did not fit
suppressors were so unpopular that most people fitted them to have a
peaceful life The elbow plug caps were marked 10,000 ohms. As an
alternative plug leads with something like carbon filaments were available.
The problem with these was that sometimes the resistance element went
much higher or went completely open circuit. There was then sparking inside
the cable which meant that there was not enough spark left to ignite the
fuel.

Maybe these leads supplied today are more reliable but I prefer solid
copper leads with resistive plug connectors. Sometimes you could fit a set
on the end of each lead but just one in the lead coming from the coil to
the distributor is fairly effective. These were supplied with male and
female threads so could easily be fitted into early Lucas distributors

Best regards

On Thu, 21 May 2020 at 16:49, Gil Rockwell <gilrockwell at gmail.com> wrote:

> Hi Lin,
>
>
>
> These are resistance wires to suppress ignition “noise” and that reading
> is fine, around 800 ohms, based on the fact you’re using the continuity
> scale.  Check the old one, it should be similar assuming the new connector
> pierced the insulation and into the core.
>
> The only wires that will register a low resistance reading are solid core,
> copper conductor wires, which cause extreme static in the radio in the car
> and the cars around you, which is why manufacturers switched to the
> resistance or “suppression” wires.
>
>
>
> Gil
>
>
>
> *From:* Healeys [mailto:healeys-bounces at autox.team.net] *On Behalf Of *Linwood
> Rose via Healeys
> *Sent:* Thursday, May 21, 2020 10:56 AM
> *To:* healeylist
> *Subject:* [Healeys] Distributor to spark plug lead continuity
>
>
>
> Hi guys,
>
> Educate me. When doing some preventative maintenance, I pulled a spark
> plug lead out of the radiator cap (using a 123 distributor) the cable
> pulled away from the terminal - not a particularly unusual outcome. Got a
> new 90 degree terminal and crimped it on to the cable (Pertronix cable) and
> before I put the boot on the end of the cable I thought I would check the
> continuity. It barely dropped below 1.
>
>
>
> So then I checked a brand new, never used, cable made-up by AH Spares. As
> shown in the image below when the sensors are attached to each end of the
> cable I get a reading of .792 which is not sufficient to even sound the
> beeper on the multimeter device. I suppose there are degrees of continuity
> (not just on/off) but I guess I expected the alarm to sound and the reading
> to drop to near zero.
>
>
>
> Could someone interpret these findings for me?
>
>
>
> Thanks, as always.
>
>
>
> Lin
>
>
>
>
>
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-- 
Best wishes

John Harper

AHC UK 100 Register Secretary
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