6 or 12 will not matter, I can power rear trailer brake lights of a 9 volt battery, just find your base socket to match, The problem is you will need a electronic flasher for 6 vlts im not sure if they make one
Or you need to run a diode between your wires to get a positive signal to funtion.
Cheers
there is a company called Vision lighting part# hil1157r they are some nice bulbs, have led's all around plus and the top of the bulb. Not many other companys do that stye nice light
Grote makes the 12 volt flasher #44890 3 terminal
Automatically adjusts to LED current, Rated from 1.0 to 20 amp, steady flash rate for all LED aplications.
But the Voltage is 11 to 15 Volts up to 25 max
So i dont know how a 6 volt would operate. Once you try using a std flasher onto a LED application The flasher can not read the low voltage so is will flash like a bulb is out. But worse case im sure you could design a seperate system of operation for a rear light setup
Other option is a Vision LED kit Part# HILRESISTOR which is just a Diode stabilizer for the voltage
If you know a electronics shop it might be cheaper than the HILRESISTOR its rather pricey.