[Mgs] Won't start

Monte Jane Morris montejane at gmail.com
Thu Apr 25 08:24:55 MDT 2013


Paul,
You've probably "hit it on the head".
Yes, I do have a points dizzy (from a 74B) that I've used for about ten
years now when I converted to HIFs. I never changed the wiring at all when
I did the conversion and kept the original coil. There is a "drive
resistor" (Moss #131-560, pp. 86) still wired in.
When I replaced the original 79 coil back in 2004,* I used a 79B
replacement at the local parts store*.
Therefore, I would assume that the coil is shot and that's the cause of my
problems.  I should now replace it with one from a 74B, correct?  When I
install the new coil (Moss#143200) do I just disconnect the drive resistor?
Will anything in the ignition have to be adjusted with the new coil?
I guess having the wrong coil does not affect (effect?) the performance of
the car since it runs real well (when it runs:)?.


On Thu, Apr 25, 2013 at 3:38 AM, PaulHunt73 <paulhunt73 at virginmedia.com>wrote:

> I'm wondering whether you mean the ignition relay doesn't click when you
> turn on the ignition.  The starter relay doesn't click until you turn the
> key to crank, and is drowned out by the solenoid clicking if not the engine
> cranking.  I presume the engine is cranking?  Originally the coil was
> powered from the ignition relay, and if that isn't operating then you would
> have no spark, but you would have no power on the second fuse up neither
> would you have battery voltage on the coil +ve.
>
> You say your car has a dizzie, but they all do.  I'm assuming you mean it
> has a replacement points dizzie of some type.  If so, then it all depends
> on whether the coil and coil wiring was changed when that was fitted.
> Originally your car would have had a length of resistance wire (the ballast
> resistance) in the harness in series with the coil.  With the points
> closed, and ignition on, if that circuit is good you should have 6v or less
> at the coil +ve, not battery voltage.  Battery voltage there implies there
> is no continuity through the coil, the points, and the distributor earth
> wire, or maybe no ballast resistance.
>
> Late MGBs with the 45DM4 distributor may well have had a 32C5 coil, which
> may have measured as low as 0.8 ohms on the primary.  Using one of these
> with points ignition, or some other non-standard ignition system, could
> well result in significant overheating and damage to the coil.  A 0.1 ohm
> coil, if that is what you are saying you have, has either gone
> short-circuit or is completely the wrong coil and is one intended for
> modern electronic systems that use a very short pulse of high voltage.
>  However you need to remove the wiring from the coil before you can measure
> its primary resistance as there are other components on the wiring that
> goes to it that will affect the reading.
>
> You are going to have to go back to first principles and determine whether
> you have the ballast resistance in circuit or not, which will determine
> which type of coil you should have.  If your coil doesn't measure up to
> that it has probably failed and will need replacing with the correct one.
>  Then you will need to check the circuit through the points and the
> distributor earth wire, as excessive current that is enough to damage the
> coil will likely damage these as well.
>
> PaulH.
>
>
> ----- Original Message -----
>
>> Any suggestions of observations from the above?


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