Using the Battery as an Electrical Tester

[Lachrymologist]

Hi all. I'm getting ready to install my JDM headlights and saw a post in the thread stating that one can run jumper cables from the battery to directly test the functions of each wire on the headlights. I'd like to do this to avoid any hassle when I go to wire everything up, but I'm not entirely sure how to properly complete a circuit to make this work.
I tried running a cable from the positive terminal to a headlight wire, and one from the negative terminal to a metal screw on the headlights. I also tried running from the chassis to a metal screw on the headlights with no luck.
Any help would be much appreciated.

[Dmang]

Did ya ground the bulb out in the assembly? Sounds like a ground issue maybe. Looks to me like there is a hot and then a powered low beam and high beam, maybe you need to run both the constant and low or high beam hot to the positive. Just a guess, be carful though. I did just use that trick to check the motors on my power seat.

[02_Legacy]

The head lights are plastic so you you can't run ground to the assembly or it won't go anywhere. If I am not mistaken the headlights have a common power source, where you need to hook positive. And then the high and low beam each have their own wire that you need to hook ground to.
But you need to hook ground directly to the wire not to a bolt on the assembly.

[dodik]

get yourself a multimeter they are anywhere from 5-15 bucks in most stores. to check that you do have a complete circuit you test for resistance in Ohms, if you get a reading that is less than OL (overload) then you have a continuity or a circuit give 12v to those two wires and see which bulb lights up, repeat the process and you'll know which wires correspond to what.

[loganmossmusic]

You cannot ground to the screws, only to other wires.
https://sl-i.net/FORUM/images/imported/2011/05/jdmprojector04-1.jpg
Just hook up the positive to the power, and experiment with ground on the other wires.

[goodnight1985]

If you don't understand electricity and the associated dangers, I wouldn't be using the battery with jumpers to test headlights with 14 ga wire.

If for any reason, you ground the positive side of the battery (with big, clunky jumper wires), you can cause some serious damage. You should always test your electrical work as if it is being used properly. Build the wiring harness and install the lights. Then test the circuit. It might take longer, but it is much safer and cleaner in the end.

[loganmossmusic]

If you don't understand electricity and the associated dangers, I wouldn't be using the battery with jumpers to test headlights with 14 ga wire.

If for any reason, you ground the positive side of the battery (with big, clunky jumper wires), you can cause some serious damage. You should always test your electrical work as if it is being used properly. Build the wiring harness and install the lights. Then test the circuit. It might take longer, but it is much safer and cleaner in the end.

This is true, it would be safer. Another idea is to do what I did and use a small 12v battery. That or disconnect the car battery from the car so that you cannot ground it out and break anything.