The board you are referring too is the control board that i mentioned in the PM,
You ought to be able to test via that connector using 12v as the board will have the correct load / resistance to allow you to do that.
There is no mention of LED's in etka as the pcb's are not for sale seperatley which is a joke.
If you change all the leds for brighter ones you will then have an imbalance with your inner / outer lights so unless you changed them all you would be best trying to match them the best you can.
farnell or RS components must have what your looking for IMO
I had a quick look through RS and filter out most of the irrelevant ones, you can further refine the search using the dimension filters to the left side.
RS Online
If you look at the forward voltage on the specs of the led's most of them are 3v some more some less so the battery pack you have at 6v may well still do damage to the led's if you are testing individual led's
Hope that helps