Newbie Disclaimer: I am not an electrical engineer, but I am very interested in the field, so forgive the naive question.

I have a set of halogen lights, like off-road lights for a car. I know nothing about these lights. I would like to figure out the amperage they'll put off when connected to a 12V DC electrical system.

So I was thinking all I need is to determine the resistance and then I could do the I = V/R formula and poof there I go.

I don't have the lights at home with me, but for a quick proof of concept I grabbed a household light bulb, 120V 60W, regular old bulb. So I figured out the amperage for that with I = P/V (60W / 120V = 0.5 amps). So to double check those numbers I grabbed a DMM, switched the range to selector to the OHM symbol, and touched the leads to the contacts on the light bulb, it finally gets a steady reading of 17.5 OHM. My calculation says that for the above formula to be correct you would need to have a resistance of 240 OHM.

Is there something that I'm not aware of in all of this? Is a digital multimeter not the right tool for this? What is the best way to determine the amperage for these lights? I want to choose the correct switches, relays and wire gauge for all this.

Thanks for any advice in advance.

Nate