The relay wasn't there. Got schematics, advice from Ronnie Bowman, online tech at Tractorsmart.com. On a BX2200 there's no timer relay. This solenoid has 2 coils, 3 wires. High current winding pulls plunger in when starter operates. Low current winding works from key switch when in on position, holds plunger in and allows fuel to flow from the injector pump into engine.
Solenoid can be tested by resistance. High current winding between white and black wires has 1 ohm resistance, low current winding between red and black wires has 1K ohm resistance. Low current winding bad, open between red and black. Verified by manually pushing plunger in while supplying 12V across winding. Plunger must remain in or solenoid is bad. Mine popped right back out again. Thanks Ronnie, and all the group members who responded to my newbie post.
Jack