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Ignition coil diode

To: <>, "MG List" <>
Subject: Ignition coil diode
From: "Tim Economu" <>
Date: Fri, 24 Sep 1999 09:41:44 -0700
The points will open and close to pulse the 12V power to the coil + terminal
(assuming this car has the original ignition, not an electronic upgrade),
which then by nature of transformer action provides a high voltage pulse to
send back to the distributor cap to be distributed to the plugs by the
This new component you see is a 100 microfarad, 50 working volt capacitor
and will act to "smooth" out the pulsed power to the coil which will
actually cause a lower voltage output from the coil high voltage side (the
fat wire in the middle), resulting in a thinner, smaller spark at the plug.
I would leave it off. The only good it may cause is that it may help
suppress RFI, or radio frequency interference so that the radio has less
static. But this is an unacceptable trade-off. Just buy good plug wires and
resistor plugs if you need this feature. Or just filter it at the radio with
an LC filter (avail. at Radio Shack).

Tim Economu
'69 BGT mona

> Kent said:

Date: Fri, 24 Sep 1999 01:56:23 -0700
Subject: Ignition coil diode?

On my '69 MGB/GT, I've always been curious about the small electronic
component the PO attaced between the ignition coil (+) terminal and
ground.  It's a small cylinder w/ the following detail:

    (+)  100uF   50WV  | (-)

where  |  is the black band on the negative(-) end of the cylinder.

What is this, and its purpose?  Is it recommended?  One of its leads
broke... should I replace the component w/ the same type?

'69 MGB/GT

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