I think you have a couple things wrong here. First off, the STC-1000 isn't a PID, it's just a simple temperature switch. There's a bit more to a PID. Also, I believe it will only work with a negative temperature coefficient (NTC) thermistors; it won't work with an RTD. As for the relay, is it AC? If I'm reading the specs on your SSR correctly, it requires DC to trigger the switch; assuming you have the 120v AC model of the STC-1000, that might explain why it's not working.