You've got it backwards, the "can" that is at the back of the main trans, between the trans and o/d unit, is the solenoid. The other one is the governer switch. Both need to be hooked up correctly to allow for o/d operation.
You can use a headlamp relay in place of the factory type, I used a Standard/Blue Streak part #LR32, along with a dash mounted switch to shut the power off to the o/d when not in use.
While you have it apart, check the balk ring, they tend to lose their tension, and can prevent the o/d from working. I wasn't able to find replacements, but they can be squeezed back to get the tension needed.
