MG Car Repair: 1978 MGB Electrial, brake failure, glovebox

Question
Engine starts and runs. Cannot turn off. Disconnect all wires from ignition switch,ignition switch relay and still have 12v to coil. unplug wire from coil and engine dies and wire go dead.

Answer
Hi Dennis.  What a wierd problem.  I presume you have a 1978 MGB made to USA specification.  This has all sorts of extra wires compared with a UK car.  My immediate reaction is that a relay is sticking on, providing power when you cut the ignition.  However, you unplugged all the wires from the ignition relay so it isn't that one.  I would start the car and then systematically unplug things until I found the wire causing the trouble.  

For example, there are two wires connected to the + terminal of the coil.  Which of these is providing the power?  The one directly to the starter or the one that goes via a resistive wire to the ignition relay and other places?  

I am suspicious of the diode that is in the brake failure circuit.  If that failed it might cause this problem.  It is hidden behind the glovebox.

Have you done anything to the car recently?  Anything at all.  I once traced a wiring problem to the fact that the owner had fitted sheepskin covers to the seats!  Admittedly, it was a Volvo with heated seats.

Keep tracing and let me know how you get on.