New truck O/D question

[PHAT TONY]

I picked up a 1971 Chev 1/2ton for prolly 30 cents on the dollar, owner knows NOTHING of the truck he's had for 17-18 years AND had restored(repainted with MANY new parts) while overseas in '04/5. "3 speed auto?" I says; "yup, original trans rebuilt" he says, on the ride home I count the tranny hit 5 times every time....o/d with lock up convertor, 700R4 pan apon home inspection, but the convertor seams to lock up between 3&4(3 hard shifts, 1 soft, 1 last hard)...and NO wires from the trans. I've got a 700 in my Blazer with a B&M thingamubob for conv lock up, nothing in the 71-I've looked everwhere!! The electric plug on the side has no connector even! Is there a way to lock it up internaly without power? Older non-electric trans? I don't know and am looking for something here....