You mean there is a relay kit installed?
Check the fuse for the power wire that feeds the relays; also check the wire for the negatives;
both would typically come directly off the battery connections if an EB (or similar) relay kit is installed;
since you replaced the battery ensure that both the positive AND negative for the headlight bypass are both connected at the battery
(either of the wires may have dropped down and you didn't notice it when reconnecting)
If you have an Eastern Beaver kit it looks like this:
http://www.easternbeaver.com/Main/Bike_Specific/Triumph/triumph.html
Those relays sit just behind the steering head;
Note that you have both a negative and positive lead that connect to the battery, the positive is fused.
If either is not connected lights will not work.
Also some kits have a 'cut' switch on the low beam only; you can elminate that as source of issue by simply switching to hi beam; if hi beam works, look for the low beam switch