MG Car Repair: mgb will turn over but wont stay running, wiring loom, starter motor

Question
My car was made for the USA.  It is a 1977 mgb. It will turn over and start but when i let off of the key it will not stay running.  I ran a wire from the fusebox to the positive side of the coil and when I turn the key the car will stay running.  I replaced the ignition switch but it still does it.

Answer
Hi Perry.  There are two main possibilities here, plus a third one.  

When you turn the ignition on without starting the engine, does everything else still work, such as the wipers and the heater motor?  If these are also not working then the problem is a faulty ignition relay.  There are two small canisters hanging down near the fusebox with 4 wires going into it.  One of these will have one wire which is white with a brown stripe.  Relays are cheap, so just replace it.

If the wipers and the heater motor are working OK then I would check for a wiring fault inside the wiring loom.  There are two white wires with a light green stripe, both attached to the + terminal of the coil.  One of them goes directly to the starter motor and this one is only live when you are starting the car.  It seems to be OK.  The other one disappears inside the wiring loom.  It is attached to a resistive wire covered with a cloth sleeve that is coloured pink.  At the other end of this wire it is attached to a white wire with a brown stripe that exits the wiring loom and attaches to fuse #3.  Somewhere along this wire you have a fault.  Note that the resistive wire is not made of copper, so you cannot solder it.  If one of the connections has broken, just shorten the wire a little, strip the end and re-attach it with a crimp terminal.  

The third possibility is a faulty diode, which is more difficult to fix.  Check both of the above and if you still have a problem get back to me.