ignition problem?

[PAISLEY@vms.cis.pitt.edu]

Quick brainstorm for all you seasoned MGB mehanics.

I have a '77 MGB that will not shut off at the key.
In order to shut the engine off I have to pull the coil wire.
This happens mostly when it's cold and wet out which in Pittsburgh right
now is just about every day.   

Where should I start to trouble-shoot?  Wiring harness, relays?
Any ideas?

Thanks in advance,

Kevin Paisley
Univ. of Pittsburgh