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MG MGB Technical - And it just kept running,,,,,

I know I've seen another thread on this but I can't find it.

I'm refurbishing an 1977 MGB someone else started. Just got the engine going but when I remove the key it keeps running. This is not dieseling. I have to pull the coil wire to shut it down. There are open wires everywhere. The question is where do I start looking? Thanks.
BJ Denis

Just thought that a second problem may be related. To get the fuel pump to work I had to wire the positive right to the battery. I suspect both issues share the same problem. Any thoughts and suggestions are appreciated.
BJ Denis

BJ - The fuel pump is powered from the same power source as the ignition is - the ignition switch. By wiring the fuel pump directly to the battery, unless you removed the original wire, you have effectively by-passed the ignition switch and have ignition power on all the time. I would suggest taking some time and getting all the wiring straightened out before going any further. All of those open wires are a disaster waiting to happen. If one of them has power on it and shorts to ground, you will watch your whole wiring harness go up in smoke long before you can get to anything to shut off the power, particularly if you have a wire (other than the one intended) going directly to the battery. Good luck - Dave
David DuBois

(I wrote a response in your other thread, but I'll take this chance to try again.)

David's right - you need to take care of all the "loose ends" (literally) and make sure everything is connected to what is should be. I'll second the warning - disconnect your fuel pump from the battery! Even if the later cars don't have a fuse in the fuel pump circuit (I know the 72 does not) you shouldn't have the fuel pump powered continuously.

The MG engine is not shut down by turning off the fuel pump, however. The B+ to the coil is switched off.

As I said in your other thread, I suspect your engine keeps running because your ignition relay is supplying power to your igniton coil, while the alternator "charge indicator" wire is keeping the relay engergized with the ignition switch off.

The ignition switch should switch the relay, "charge indicator light circut" (from ign switch to alt, via dash light) and the ignition coil. Otherwise, you have a "latch" created.

I inadvertently did this to my car,and it is startling to turn the key to "off" and have your engine keep running!

Get a good wiring diagram - you'll need it.

The Haynes Manual has the same wiring diagram as the Bentley manual, but the Bentlye manual is more usefull for everything else.

These guys are more knowledgeable than I, so they may know additional resources.
Matthew Jones

Also, get the wiring diagram and list of "wires to components" and "components to wires" from www.mgbexperience.com. Go to Kinko's or someplace with computers and color printers and print wiring diagram as large as you can afford, then laminate it. Makes it a lot easier. Print the wire listings in color too...really speeds up the diagnosis process.
J.T. Bamford

North American spec cars with an ignition relay (75 on or so) have a wiring design fault that means that if there is any problem in the emissions plumbing or anti-runon valve the engine will continue to run normally with the ignition switch off. Having said that, wiring direct from the battery to the fuel pump will also keep the ignition relay operated, and hence power to the coil!
Paul Hunt

This thread was discussed between 23/07/2003 and 25/07/2003

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