I am still in development. There are still a few bugs left.

Without prising myself, but I don't think that a DIY guide would help anyone who would not be able to do this also without such a guide.

The "interface module" is not just a simple box with some wires and a relais.
It contains a complex PCB Layout, a 20MHz 8bit-Risc microprocessor and some SMD electronic devices.
Programming the processor equires a lot of know-how in microprocessor and automotive can-bus architecture, IR signals, etc...

But I plan to sell a plug&play package in the future.