The T3000 uses digital relays that are sensitive to current variation.
The Y and W wires should be isolated. (In this case at least the W, since I’m guessing that is what is tripping yours, heat mode)
Thermostat W wire should connect to trigger input of the relay, along with Common. Then the Isolation relay handles switching the 24VAC across its relay to the W terminal on the HVAC board.
The goal is to have the relay switch the power drawn by the HVAC and not the Thermostat across the W.
There is not really a schematic for this. It will be a bit different what is needed from system to system. Here is something quick and dirty, only the terminals applicable to the W isolation:
