Have they worked since you added your homemade switch? Why did you need such a switch? I take it you just tapped one (both?) of the ecm leads to complete the ground(s).
So you have 2 constant hots at each relay. When the car gets hot, is there signal at the relays (ecm should complete ground side of circuit)? You want to rule out the relays, the fuse & fusible links and work backwards. If the relays are good & the sensor is new, I might guess the ECM is a problem. Chips don't partially fry.
Are one of these diagrams right for your car?
GM LT1 early:
GM LT1 later:
