Engine Starts With Light Switch

[Mad Dog]

1979 MGB When you turn on the light switch to headlights the starter will crank. When checking white wire with blue tracer in headlight bucket wire showes it is conected to ground. Any one have this problem? Answer

[Art]

People have done some pretty wierd things over the years to protect their cars.  The most common other of these I have run into on later cars is a single position switch (on/off, usually an umarked fog light switch) in the OD switch position on non-OD cars hooked to the tach wire.  With that connection open, the starter will turn, but the ignition will not fire and the car won't start.  This would be an "active" measure as the switch must be on and requires you to shut it off  to arm.  The car will not run with it open, even after starting.

This could be someone's idea of a passive security measure.  I would suspect this if the car continues to run when the switch is turned off, so it only effects the starter.  I call it "passive" because it automatically secures the car when shut down until you turn the light switch on.  It is also much less obvious than an extra switch (as below).  I don't know if that was what was intended, but it seems to work that way.
 
Hope that helps you.

Art