[Mgs] Won't start

PaulHunt73 paulhunt73 at virginmedia.com
Thu Apr 25 02:38:02 MDT 2013


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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