Starting/running problem

Here goes, so I took the old girl out for a run and about a mile and half from home she just cut out, luckily at a junction. She would turn over and start but as soon as I let go of the key,died. Rightly or wrongly I drove her home with the key turned and it was not a pretty sound as the starter was turning😬. Anyway at home same problem so I initially thought it may be the ignition so I changed the switch, same outcome ☹️Then I checked the pump relay, the pump by bridging the relay, multimeter on the wiring to the relay, wiring to starter and alternator, all ok🤔I'm stumped and feel it may be something simple as when I start her and keep the key turned she starts and runs but the second I let go she dies, any suggestions welcome thanks 

With the ignition in the run position (not cranking) are you getting 12v to terminal 15 on your coil?

I'm guessing you have an older car with points so do what Steve has suggested and check the power supply to the coil which probably will be not be there.
The cause of your trouble is more than likely going to be the ballast resistor wire which will have broken. I would fit a 12v coil, you should have a 9v with ballast resistor ignition, and run a new standard wire.
The other solution if you do have the 9v coil is to buy a resistor on ebay, they're about £5, and run a new wire to the coil with that in the circuit.

My thoughts exactly Cedar, sounds like it's starting off the 15a wire from the starter. Maybe he has a 12v coil already fitted and this may have burnt out the resistor wire.

It's got to be that hasn't it, it's running on the ballast by-pass circuit.

Hi guys, I have a 12v coil on the car and when checked today with the ignition turned on not cranking was only reading 4v at coil? Thanks 

Are you running points? Or was the car running points originally? If so, as above you may have a bad resistor wire. Just for a test run a wire from battery positive to terminal 15 on your coil and see if it runs. By the way are you a fellow Stokie?

Ok thanks Steve I will try that, car originally was a 1.5 gl I think, it's now a 9A/KR hybrid 😁, I am a fellow Stokie but moved to sunny Cornwall 3years ago👍

Had similar  problem with my gti which has stood garaged over winter.changed metering head twice same problem.Basically put 20l fresh petrol in with fuel system cleaner and opened each injector line on the head and bled system,BE CAREFUL. Finally got it going.when metering head dried  signs of flash rust so think had condensation etc in fuel tank.

Now you've mentioned it's an engine swop, be careful what you do! With not knowing the setup do some more research before putting any power to the coil.

Can you post pics of engine, coil, coil wiring, distributor(if it has one), starter motor wiring.