1) Amps = Wattage / Volts. Also, normally you lose wattage going from AC to DC. IIRC it is around 20% lose. So 80 watts will become around 65 watts.

If I did this I would put two full wave bridge rectifiers one on the front light yellow wire and one for the tail light wire which includes the lighted whip.  The 20% reduction would occur after each bridge rectifier so the 36W head light would then require43.2 watts and the 5w tail light & the 25watt whip would pull 36 watts for a total of 79.2 watts required.

 

A simple diode will not fix this as it. A full bridge rectifier will help.

They make different types of bridge rectifiers, a diode based and a silicone chip based one, both are bridge rectifiers with full wave rectified.
https://en.wikipedia.org/wiki/Diode_bridge




Doing the math on this system at 12V would yield 6.6 Amps (79.2/12), stock system is about 60W/12V = 5 Amps  (55W headlight + 5W tail light).

Does anybody know if 6.6 Amps would melt the stock system?

I've also heard you can get a 95% efficiency full wave bridge rectifier, any truth to this? 

If so that would reduce my wattage intake to 69.30W & 5.78 amps @12V and with a LED tail light bulb I could get it down to 65W & 5.43 Amps @12v  Which I think would work on the stock system without a battery?


Also what gauge wire is the wiring system built out of?  14ga?
I can check amp rating by gauge size.