Hi i recently purchased a Technics RS-X911 cassette deck and i later realized it was designed to be used with a Technics amp which is also the power supply for the unit. On the back of the unit there is a 3 pin connector. I wanted to ask if anyone knows anything about doing this conversion, for example the pinout of that connector. I read that there are meant to be 2 12v lines to make up the 24v but i am not sure of that and on which pins that is meant to go.
You've apparently purchased a cassette deck that was intended for a "Rack System". Racks were very low grade systems put together with a price point as their own guide to quality.
I can't help you with specific pin allotments. Rack systems came and went every six months so there's no telling what your unit requires. Most had only minimal service manuals, as they weren't truly intended to be repaired. No shop would hold onto a manual for a rack system for more than about two years as the customer would have been told there was no point in putting money into repairing the system.
At this point I would suggest you just buy a cassette deck that is meant to be a stand alone unit and recycle this one.