Al:
Just an idea here: does the ovedrive button always do what it's supposed to do? I'm wondering if the shifter lock button is somehow interfering with the wiring from the O/D button, to the point where, when the lock button is depressed, it causes the O/D switch to "break", from its normal operating position, which is continuity through the O/D circuit. Perhaps the faint click you hear is the O/D relay changing position. Have you tried depressing the lock button whilst driving in top gear to see if it'll cause the O/D to disengage (you probably have...). As far as the bulb failure light is concerned, a glitch in the O/D wiring might be enough to throw an odd load - somehow - into the lighting circuitry. Do ALL of the other indicator lights in the dash function properly?
I've got over 280K (clicks) on my '88 700 and I'm pretty confident that there's no (intentional) electrical activity associated with the shifter lock knob.
Standing by.
Garth