Technical 58 Cadillac Petronix power relay problem

I just fitted a Petronix power relay to my 58 Cadillac prior to fitting the ignitor II
but as is mentioned in their leaflet you might not be able to turn it off with the key until the diode is fitted, ok if you have a Ford or GM external voltage reg with 4 posts
But....the Cadillac only has 3 ...anyone know for definite where to connect the diode to stop return current from the regulator returning back to the Power relay, keeping the car running with key off...

Id like to stop engine with the Key

thanks in advance