[John Poling]

S_

A relay does not "cut down" the amperage from the battery. The only thing the rating on a relay tells you is that more than 15 amps pulled through the realy could cause it to stop working correctly. If you do not know the amperage a certain component pull, you have to take power (watts) into consideration when figuring whether or not a relay will depedably work or not.

P=Power (watts)
I=Current (amperes)
E=Potential (Voltage)

P=IxE
I=P/E
E=P/I

A 12 volt cars voltage supply is normal at 12.7 volts from the battery.

OEM headlights or most foglights are generally rated at 55 watts.

Therefore using the appropriate formula from above one could deduce that the current draw would be equal to about 8.66 amps for two headlights on their low beams.

This is just an example for you to use.

The 750 amp rating on a battery is just basically letting you know the "Power Ability" of the battery, kind of like your typical house circuit breaker box has a 100 or 200 or whatever ampere main on it. This is the amperage value that you wont exceed by supply.

What are you testing?

John