Ignition wont turn off intermittently.

[micky342]

Good evening this is my first post on this board although I have owned a number of classic cars over the years.

I have bought a P5B coupe which has excellent bodywork but is an incomplete restoration and hasnt been on the road for 22 years.  I have fixed many of the usual problems such as brakes, rubber components and ignition etc but the following fault has thrown me.  Earlier in the process I had difficulty starting the car but in the process thought I had turned the ignition off.  It was only when sometime later my hand came into contact with a very hot coil I discovered the ignition was still on regardless of the switch position.

I subsequently replaced the ignition switch and thought all was well until today.  Having got the engine running sweetly I went to turn it off and no surprise it kept running again the key position was irrelevant.  I took off the low tension side of the coil which stopped the engine and since trying again all is well.

Thanks for any replies

[johnwp5bcoupe]

Hi Micky welcome to the forum I can only assume the ignition is being fed (hot wired) from somewhere apart from the switch or the switch is wired incorrectly?
It should be fed from pin 2 on the switch which is a white wire which went to a ballast resistor (may not be there?) then this turned into a white and purple also at this point a wire ( originally ) again white and purple came from the starter motor to prevent voltage drop when starting.

[richardlamsdale]

Hi and welcome. Stating the obvious but its very strange this happens intermittently. There were numerous changes to the ignition circuit during the life of the P5B, with ballast resistors and thief-proof coils, so difficult to answer without knowing the specifics of your car.

You probably know this already, but I'd suggest getting a decent wiring diagram from the club, and working backwards from the coil when you can cause the issue to re-occur, to work out where the coil is getting power from. If there's a ballast resistor don't forget the coil can receive power from two places - both from the starter motor during starting and the ignition switch via the ballast.

[johnwp5bcoupe]

Reading the post Richard it's not intermittent but permanently on?

[richardlamsdale]

You may be right John - that would make more sense, and hopefully make it easier to trace.

[micky342]

John.  Thanks for your earlier post and kind welcome to the club.  The fault is intermittent, I did initially wonder whether it was the ignition relay but looking at the workshop manual wiring diagram I am not so sure.  The detail is very small and I think I need glasses like Billy Bunter to make out the layout.

I will change the relay as the contacts look rusty and generally in poor condition.

I gather from previous posts that a larger W/D is available to club members but unsure how to obtain it

Once again thanks for your help

Mike

[micky342]

Thanks Richard and for the welcome and advice. 

There is no evidence of a ballast resistor however there are two leads to the + side of the coil, I am assuming one is the live feed and the other for the tacho but until I can get a better sized wiring diagram I will have to monitor the situation.  The colour of the leads is difficult to make out no doubt time and heat has faded the original colour

Mike

[johnwp5bcoupe]

There is no ignition relay as such you have an inhibitor switch which controls the start relay which fires the starter solenoid!

Email sent!

[lagain]

Is it affected by turning the steering wheel ?

I had only had my car a few years so it was probably 1979 !
I think from memory that it would cut out and I found that a wire was traped in the steering column

[micky342]

No, its still stationary in the garage with no movement of the steering wheel.  Thx for the suggestion though
Mike

[Phil Nottingham]

Wiring diagrams for the early ballasted coil/ignition switch on the console are available to members. Email me with your number and private email specifying whether you want lined colour or colour coded version

[micky342]

Phil - E-mail sent.  Many thx


Mike

[Phil Nottingham]

Sent