The UCH is a multifunction unit. It's a microprocessor controlled logic box filled with numerous micro-relays that turn on/off all the things you take for granted such as electric windows (up/down)' central locking (lock/unlock), lighting (side, dipped, main beams, indicators and hazard warning), security and access as well as it being the main multiplexing hub for the various controllers on the cars Canbus network (ECM, ABS/ESP, SRS, HVAC, EPAS, XENON)
Yes you could wire a so called simple circuit but it's not as simple as you'd think especially if you want it to look OE.
Personally, I'd say if it needs a new UCH that you have it replaced. You need to find out why yours has gone though... Age is becoming common now for failures but so is water ingress and if it's water damage, failure to fix the issue, will result in money wasted and the new parts warranty being voided.
Mick