hey i bought some gauges and i just have a couple of questions.

For the Voltmeter gauge.... where is the best place to wire it into a 12v source? ive read that doing it directly to the battery drains it. Is that true? If so where else would be a good spot.

And for the oil pressure gauge, where is the oil psi sending unit located in the car? Once i find it do i just unplug it then plug in my new line?

Thanks in advance.