Well lets do the basic checks then see if you can find something.
Check pin 7 RD/BK wire at the servo and make sure you have battery voltage with key on.
Check pin10 BK for ground.
Check pin 9 LB/RD should have battery voltage and should go to zero with brakes depressed.
Yes a test light will do just fine. Also hook it to battery postive then check pin 10 to make sure your ground is ok
You have a bad brake pressure deactivation switch. Here is a pick of where it is. It is just under the master cylinder and it is a switch with a 2 wire plug the wire colors are LB/RD on both sides.Find brake pressure switch at location A7 and trace it down. It should have power accross both wires until brakes are depressed.