William,
The primary should either show a very low resistance or the resistance
of the ballast resistor. I think that the 5.6ohm measurement indicates
an internal ballast. So, the question is, does your car have an
external ballast resistor?
The secondary of an ignition coil may show infinite resistance with a
meter, and still work. This is because when they made these coils
originally, they allowed 3 breaks in the secondary when winding. The
secondary has a thin insulating layer, which is sufficiently thin that
it will break down when operating, allowing current to pass. When the
wire broke during the winding process, they twisted the ends together
and continued.
The coil may well be OK.
Simon
On Sun, Feb 25, 2024 at 4:24â?¯PM William Killeffer <wkilleffer@epbfi.com>
wrote:
>
> Hello everyone,
>
> My car's a 1974 MGB with an 18GK engine and twin HS4 carbs. I've been running
> a Pertronix distributor with its matching coil for awhile, but just got the
> car's 25D back from Jeff at Advance, and it looks better than what it
> probably did when it was new. I'm going to go back to using points and
> condenser with the rebuilt distributor.
>
> I still have the factory Lucas coil that came with the car when I first
> obtained it. I checked the resistance to see if it was still useful, and
> here's what I found:
>
> With a small handheld analog meter, it registered around 6700ohm across the
> secondary, and the little meter's not capable of giving a reading for the
> primary.
>
> On the new-to-me Sears Engine Analyzer, the primary shows 5.6ohm and the
> secondary shows 5100ohm.
>
> Either way, that looks too high given some of the other numbers I've seen. I
> haven't checked the Pertronix coil, but will before trying to use it.
>
> Am I right in believing this original coil shouldn't be used?
>
> Thank you,
> -Bill
> Sent from my iPhone
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