You do not say which one, many different Ref No's during the production of these beasties. However this link will have the right break down for yours once you have ID'd the ref No.
Lgb service manuals - Model Train Forum - the complete model train resource
What it will not do of course is not give you details of how to install a chip. However there have been quite a few that have posted on how to install a chip to varying locs on this forum. Once you know the type you then need to understand the method, I can think of at least 3 ways (there may be more).
1 Old types with common wire for a motor and one rail, fairly extensive rebuild.
2 Decoder ready, just plugs in once all the Dips have been set to off.
3 A 4 pin plug to chassis, just cut out at mother board and rewire ensuring that the Motor and Tracks wires are not mixed up.
Hope this helps some.