50 Special poor lighting and brake light problem

Hi, I've just purchased a 50 special for the wife and I have been going over it and seems to run well(112cc Kit, Upgeared, race crank, race exhaust) but I have a problem with the lighting. I am only getting 1.8v at the Junction box so the lighting is weak and when the brake light is pushed all of the lighting near on goes out.

Some one mentioned to me that I should try putting LED lamps in but I assume I would need some sort of AC/DC rectifier to convert and 6v festoon led lamps appear to be not available anywhere. Problem is I'm still only producing 1.8v. Do you think it is likely to be the coil or condenser or a little of both?

Or maybe something else??

Paul.