Well, this thread is ancient but I'll update it since I finally found the problem two months after my initial post. I'm embarrassed to admit it but in the interests of maybe helping out some other Electrical Genius I'll swallow my pride.
I have checked the dash-mounted switch, and the power wire to the Accusump solenoid, probably a dozen times. They always lit up my test light so I assumed the wiring was fine and it was some other problem. Well, last night in a fit of brain activity I put the probe for my test light on the ground wire at the solenoid. Surprise--it lit the test light, as well. I moved the ground wire to a bolt on the chassis, lit up the ignition, switched on the Accusump, and voila--instant
oil pressure appeared on my gauge.
Inside the housing for the Accusump solenoid there is a hole drilled, with a screw screwed into it. The screw head is painted green and for whatever reason I've always assumed it was intended for the ground wire. Whether it is or not, it obviously did not work, at least in my case. Grounding the solenoid to the chassis has cured the problem and finally, four months after installation, I am able to pre-lube my engine. Better late than never, I suppose.
Thanks to all for their suggestions.
Bob