The Rear and Sub pre-amp has nothing.

Those Android radios can be fickle. There are a lot of different models using the same board that have different features enabled or disabled. I'm not familiar with the "P3-T1", but it looks like the common T3-P1 defaults to a single pair of L/R preamp outputs plus a single sub output. If your wiring harness has separate front and rear preamp outputs then it might not be the correct wiring harness for that particular model of radio (or the harness simply has extra RCA jacks that cannot be used). Check with the supplier of the radio and look around online for other people using the T3. If you think the wiring harness is correct, then check the radio's settings and menus to see if there is anything that would turn outputs on or off. But my guess is the radio has only L, R, and Sub outputs and the harness has extra unusable jacks. Also be aware those wiring harnesses are very delicate so one or more RCA jacks might have become disconnected at the Molex.