Will a 55 watt 12v light be as bright as a 25W 6v if hooked up to 6v.?

No, it will not. With only half the voltage that it requires

to work it will only light up half as much. Actually, it

will light up a bit less with half as much voltage.

If you have a 6V vehicle you can change it over to

12V quite easy. The wires in a 6V vehicle do not

care about the amount of the voltage. The only things

that are affected are all the lights, the generator,

the voltage regulator, the ignition coil, and the heater

blower motor. If you change all the lights to 12V, install

a 12V alternator with, or without it's own regulator,

the ignition coil, and a 12V motor for the blower you

will have a 12 electrical system to use those 12V

halogen lights. Plus, you can always change back

to original if you would like at some later time.

One thing, though. If you use an old 12V alternator

that must have an external voltage regulator, you

must also change the regulator to one of 12V also.

If you change to an alternator with the internal

regulator, you must have the old regulator unplugged

from the system and use the ignition and power

wires from it to connect to the alternator. Some

alternators require a resistor wire inline, but you

can buy these wire 'pigtails' at most autoparts

stores. In fact, most autoparts stores can also

help to show you how to do this.

No. It will put out as much light as a 12.5 watt bulb.

No, it does not work like that.. sorry