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Why would my ignition only be live when the key is held in the 'start' position? I.e. only when the car is cranking over? As soon as the key is turned back to the ignition position, then engine stops again.
Even stranger, is that after cranking the engine over on the key, if I then turn the key back to the ignition position, obviously it stops turning, but then when turning the key back further (as if I were going to take the keys out) the engine will jolt round a fraction again?
Also, when I turn the ignition on, I only get the oil light coming on, but no red ignition light. (even though the bulb is working)
Just for info, although I dont think any of it might be related, the car has recently had an engine and geabox change (from auto to manual) and the pedal box has been changed too. This is a 1970 Mk2 estate by the way.

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Don't know about your wiring but on cars with ballast resistors then this is what you get when the resistor goes open circuit. Has the car got a 6V (ballasted) coil or 12V, mind my car should have had a 6V coil but actually had a 12V version.


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Classic symptoms of a ballast resister having gone down.  

When cranking over, the ballast resister is by passed so that a full 12V goes to the coil (typically rated at 6v) and gives a bigger spark to assist starting.  

Once the key is released to the normal running position the system reverts to a feed via the ballast resister so that the coil gets its lower (correct) voltage and gives a 'normal' spark.  Should there be a problem with the ballast resistor when in the 'running' position no current can get through it to energise the coil.

Quick dodge to check is to pull the leads off the ballast resistor, link them together (takes the resister out of the equation) and see if you have a spark and/or the engine runs.  If it does then you need a new resister ......... or look at the one in the car and see if you can identify the fault.  Typically the long rivet that holds a spade connector to the resistor winding fails in which case remove it (drill off the head) and replace with a long screw and nut as a temporary measure.  

In an emergency you can run the car for a short time (get you home if you are nearby) with the resister bypassed. However be aware that the coil in receiving too much current will get hot and eventually fail.

A word of caution about ballast resistors.  There are 2 ratings - about 2 ohms and about 5 ohms.  If using the 2 ohm one the current is not reduced as much so if used when 5 ohm is specified (as on the 2000/2500) your coil will run hot and eventually fail when it warms up ... and is a bu**er to diagnose :-/.  Been there done that.

A previous owner had fitted a new ballast resister just before he sold me my PI.  At first the engine was fine but after a week or so it started to cut out after about 10 minutes running which at first I put down to the PI system (it came with a PI system that was playing up and which is why I got the car cheap :)).  I realised eventually that the symptoms were classic coil breaking down so nicked the ballast resistor and coil of the Mk2 2000 and problem cured.  When I checked the new resistor that had been fitted I found it was the lower resistance type.


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