Hi Don,

The left flipper button has 2 switches behind it.
One switch has a Black&Orange wire and an Orange&Black wire. That switch activates the Lock relay on the schematic at 4E
The other has a Black&White wire and a Yellow wire. That switch activates the flipper.

You can find out which circuit is causing the problem by putting paper in between the contact points.
As currieddog points out, most likely the Lock relay coil is fried and needs to be replaced. You can test that coil with an ohmmeter.