[Healeys] OD Problem

[Leonard Hartnett]

On the way back from Autumn Classic in San Juan Bautista (CA), my overdrive
began acting strangely.

With the OD switch ON, when I step down on the accelerator, the OD disengages.
With OD engaged, turning the OD switch OFF causes the OD to disengage
instantly without stepping on the accelerator. I assume (oops!) that the
problem is electrical. Which component, or combination of components, is most
likely to be the culprit?

TIA

(The Other) Len
Vacaville,  California,  USA
1967 3000 MKIII, HBJ8L39031