It's almost as if the key is in the bike and turned to the on position. Except the key isn't in the bike.
The low beam is the one that comes on with the dash lights. Unless if you press the high beam button, then its the high beam.
I took all the relays out one by one (including the load relief relay) but the bike still comes on (without the key) when i reconnect the negative battery cable. I was looking for a relay that may have fused/welded it self open accidently. but I didn't find any. All the relays look very clean and the wires in the electric box seem good.
I am surprised you have not found existing solution already posted here (in older post) and also on the K1200LT forums (https://www.bmwlt.com/forums/k1200lt/
This is a well known issues on all "brick-engine" (including older K100 and K1100 models) when attempt to start with a weak battery. The Starter Relay contacts will weld together - until Starter Relay is fixed or replaced it will continue to behave like this. Like many motorcycles, the main Battery Positive wire becomes direct to starter once the Relay is activated (even with ignition key OFF , the contacts are welded in your case).
Early K1200RS have the 1st generation BLACK starter-relay. Later, BMW changed to a newer fancy version that is BLUE (with electronics added inside relay) that will NOT attempt a start on a low-battery condition - basically a work-around the original problem of welded contacts.
Only K1200RS produced after January-2001 have the newer type BLUE relay installed at factory, including a slightly different main wiring harness. All other K1200RS owners can install the fairly expensive retrofit starter kit. See this link on parts fiche of MAX-BMW for the retrofit kit - item number 1:
The OLD design starter relay (black unit) is NOT visible anymore on BMW parts fiche for K1200RS. However, because it was also used on K100 and K1100 AND was made by BOSCH, it is still available for a good price from a few 3rd party suppliers like Euro-MotoElectrics:
BOSCH OEM: https://www.euromotoelectrics.com/pr...rel-k008oe.htm
Replacement equivalent: https://www.euromotoelectrics.com/St...p/rel-k008.htm
The Starter relay is located in top electrical junction box - separate and below all other small relays (see attache photo).
Some "cheap" owners have opened the Starter Relay to file / clean the contacts so that they can re-use the old one. This may work for a short time, but is another problem waiting to happen. In addition, unless you ALWAYS have a very good / strong / recent battery, the older type BLACK Relay is always a risk.