You should be more specific or you may get some incorrect advice. When I here "old" and "radiator" I think of the old cast iron steam radiator. If this is the case, then you should not tie them together as the heating system will not work properly. If it was fin radiation with a copper tube and aluminum fins, then it is possible that you could cap them off. A question that you should also answer is how much of this radiation did you remove? Your heating system was designed with a certain heat loss, assuming you are going from an old single pane window to an insulated door, you may be alright, a glass door with less r value, maybe not. You have to remember that you still have a house to heat, removing heat for convenience may cause you grief in the future. I would suggest you find an alternate place nearby to re-install this "radiator".