Which of these wires would be positive? I’m trying to wire a fan into an existing run which feeds the lights over the dinette.
Traditionally, red was positive and black negative. Many RVs, including LDs have the black positive and the white negative.
Confusing?
Yes, it can be. I always verify the polarity with a voltmeter when it matters,
Larry
Very confusing. I figured it out, looks like white is negative. Thanks!
In RVs I've seen, white is almost always DC negative, and black or any other color is positive.
But I have seen one RV where the front half was wired negative=white/positive=black; but the back half was wired negative=black/positive=white! My friend who owned that rig blew out a couple of appliances before figuring out that the manufacturer had reversed the polarity midway through the rig. I guess two different technicians, or two different crews, had done the wiring. What a mess!
So as Larry said, always check polarity with a meter every time before you hook up anything.
In RVs I've seen, white is almost always DC negative, and black or any other color is positive.
So as Larry said, always check polarity with a meter every time before you hook up anything.
For the first 45 years of my life, in both my professional and hobbyist life, 12-volt positive wires were red and negative black..
This is the standard in automotive, amateur radio equipment, and industrial 12-volt devices, and it even extends into the RV world. Next time you are able to look at your RV's Shurflo water pump, notice the supply wires are red and black, and the black one is negative.
To make life a little more interesting, low-voltage marine wiring codes (American Boat and Yacht Council, “ABYC) show positive wires as red and negative wires as either black or yellow.
https://www.electricaltechnology.org/2020/07/marine-boat-cable-wire-color-codes.html”
Depending on the sort of device you are working on, the negative can be black, white, or yellow
Why the difference in standards? Who knows? Verify with a voltmeter..
Larry
For the first 45 years of my life, in both my professional and hobbyist life, 12-volt positive wires were red and negative black..
That makes sense. If you look in the photo I posted in the initial post, the smaller gauge wires for the little round led light above the dinette are that way. I'm learning more than I ever wanted to know! ;D Cleaning up the connections along the way.
I like the ABYC's use of yellow for negative wires, even though it contravenes a century's worth of custom. The good thing about it is that it distinguishes a 12 V negative wire from a 120 V hot wire. With that said, I'm not entirely consistent about it, just because I have a lot more black than yellow wire on hand. But in the long run, I'll go with yellow.
Help me out here, If you are wiring up a DC motor and you get the polarity reversed, won't the motor run backwards?
Thanks for the input.
Jon
Yes, it will run backward.