Barrie
The two issues with the coil may not be directly related (except in that they both involve the coil)
for all of the below, I assume that you are still running the original points system (i.e. it hasn't been replaced by an electronic ignition system of some sort)
Re the initial burning out of the coil: this can (and does) happen if the ignition is left switched on without the engine running for a significant period of time if the points are closed. under such conditions the points complete the circuit to earth and the coil draws current continuously - it will overheat after a time if this happens, just how long depends on the quality of the coil. depending on how you have the points set up, you have about 160 degrees chance out of 360 (so a bit less than 50:50) depending on exactly where in the cycle the engine stopped when last turned off.
I suspect this is what happened in this case
As a general recommendation, if you are going to switch the ignition on without the engine running for any period of time (e.g. electrical work), then disconnect the coil (sw terminal - white and yellow wire on the 407 if it still has the original colour coding)
Re the current overheating of coils: this is strongly suggestive of using coils that are designed for use with a ballast resistor without the resistor.
whilst it is a little difficult to diagnose by forum (i.e. without seeing the car), the first place i'd look is the ballast resistor.
the 407's original ignition system does have a ballast resistor (and it is bridged out during starting by a ballast relay that is switched by the starter solenoid).
I can only guess what has happened in the past, a typical scenario goes something like this:
1) coil needs replacement and a 'non resistor' coil is procured and installed by mistake - the car will start well, but run very poorly (because the resistor that is in circuit during normal running effectively halves the voltage to the coil)
2) in an attempt to rectify this, someone removes (or shorts out) the resistor and that 'cures' the problem and the car runs fine now (well it's harder to start, particularly when very cold or when the battery is getting a little tired, but it runs 'just like it used to')
3) now the mistaken coil burns out and is replaced by a correctly specified coil (a 'resistor type'), but now running without the resistor - this means that when running the coil will 'see' twice the voltage it is designed for - it will inevitably burn out
So, how to diagnose and deal with this
is there a resistor? (see the picture on john's post - the resistor is the rectangular white object with a wire on each end) in the 407 it should have a white wire attached to one end and two white and yellow wires attached to the other.
if it's there, is it connected? or has it been bridged out (e.g. a wire placed from one terminal to another)
if the resistor is all in order, the next place to look is the ballast relay - if that has an internal short or is stuck closed, then it is effectively shorting out the resistor all the time
cure - install resistor correctly and use with correctly specified coil, replace ballast relay (and verify correct operation during starting)
the (NOT RECOMMENDED) alternative to problem solving and rectifying the problem is to replace the coil with a 'non resistor' coil - this resets the car to the same state as the original 'bodge' - the car will run fine, but may be more difficult to start than it needs to be - sadly this is a common solution (one that the makers of aerostart are most grateful for :-))
hope that helps
Julian
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