Rob;

All the electrical parts and circuits controlling the OD are just for the convenience of controlling the activation lever with a simple switch on the dash...so if you disconnect all of the elec control stuff and it still self-activates, the issue is clearly within the OD itself...I'd start by opening the cover plate to access the activation lever (I'm presuming a "D" Type here), and inspecting conditions of the Sol to Act Lever connection, as well as unactivated Lever position. It should be positioned away from Sol, and have preload keeping it there...if it has no preload, I don't think this can be repaired from the outside, but OD must be removed for internal repairs of the control valving...I'd refer to an internal exploded assembly diagram next...

Good Hunting!