Easy way to test for negative or positive

[unclejemima]

Here the scoop. I have a plug with 4 pins in it. I know 2 of the pins are positive, and 2 of the pins are negative. Only problem, i don't know which ones.

...so, how I used to do it was use a automotive test light. Hook one end up to a battery negative post and then start probing the wires till the light on the tester lit up.

This worked great on 12v stuff, but on my 48v battery (what I'm working on now) it did not work so good. Blew the test light in about 1/10 of a second!

What easy way can I test to see what pins are positive and what pins are negative with just a regular multi-meter? I was thinking of hooking one end of the meter up to a battery (12v battery) negative post...then start probing the pins one at a time until I got a reading. Would that work?

Any advice would be appreciated!

 

[spinningmagnets]

Hook up four 12V car bulbs in series, or two 24V bulbs in series. They are not polarised, so plugging them in "backwards" will not hurt the bulbs. This way, you can separate the two positives from the two negatives, but not which group is which...its a cheap start.

Then use a multimeter between the bulb-set and the battery leads? Set for 0V-100V DC range?

This gives me an idea, one of the 12V bulbs can be replaced by a 12V seat-belt buzzer.

 

[unclejemima]

Ok. Very neat idea...

There must be an easy way to test it with a meter thou?

 

[unclejemima]

How about this bad boy. Its make is an audible alarm vs a light....works for 6, 12 and 24 volt...I'd imagine 48v would just make a higher pitched noise without damage as where a test light would actually blow after exceeding the recommended voltage.

http://www.princessauto.com/pal/Electrical/Audible-Circuit-Tester/4211092.p

 

[dogman dan]

DVM, positive voltage means you have the red probe in the positive, assuming the red wire is on the + plug on the voltmeter.

Negative voltage means you found the negative with the red wire.

 

[skeetab5780]

Most common digital volt meters these days will just read a negative voltage if the terminals are backwards. It will show a " - " symbol on the left hand side of the display usually

example:

 

[wesnewell]

Use a 48V test lamp or a volt meter. If you hook up an old analog volt meter backwards, the needle will peg out backwards. Most DVM's will show a - symbiol as above post.