So I disconnect the two leads coming from the PID and twist them together to test the SSR?
No, you disconnect the power wires going into and out of the ssr. Then use a wire nut (or twist and electrical tape, just make sure it is good and tight) to connect those together, then power it up - it will be the same as if the PID is at 100%. Then test with the amp meter.
Do you have a wiring diagram or could you sketch one up for us, having one would make trouble shooting this a bit easier.