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I am installing LED accent lighting, planning to replace the courtesy lights with red LEDs. The wiring to the lights is black and white. Tracing the wiring back a little ways the color is red and black! I checked at the dash switch and the color is ...orange? Just trying to make sure I have the correct polarity before I go any further. Does anyone know which would be the positive? I assume the white wire at the light, but you know what happens when you assume! Thanks for any help. Ray
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If you have a harbor freight near by then something like 5 bucks gets you a decent multimeter and you know for sure. You could get better than Harbor Freight, I would love to get my hands on another Fluke 87 but the Harbor Freight automotive multimeter with tachometer was ~30 so the boat can find another way to claim the 300 bucks saved.
If not you should be able to get something for about 30 bucks or less at just about any hardware store, home improvement store, walmart, parts store or tool supply. You could probably borrow one from a buddy or one of those auto parts places that do a rent a tool where you pay them 2 times what its worth for an old beat up tool and get your money back when you return it.
Most any of the meters will have a setting for at or near 12 volts and show you +12 or -12 when you connected to the wires when you turn the circuit on, if you dig up an old analog one that doesn't do negative for DC and when you touch the leads to the wire the needle goes down scale or doesn't move then positives the other wire. Anything else is a guess based on mixture of different colors and the fact most of the wiring was probably done by hand and it probably didn't matter which way they hooked it up on the original bulbs, although white seems like a pretty good guess in this case. -
The cool thing about 12 volt ready LEDs, although they do have polarity, is that nothing bad happens if you wire them up backwards. So use your LED light to determine the wiring's polarity. Temporarily wire the LED up, if it lites up, you know which is B+ and which is B-. If it doesnt lite, you still know the polarity, its just reversed. Swap the wires just to comfirm.Comment
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OK, I just finished wiring it up. Went to Harbor Freight and got a cheap multimeter ($3.99) and figured out the polarity. Works fine! Thanks for the replies, but already had it done by the time I checked here for answers. I didn't know it wouldn't damage the lights if wired backwards, that is good to know for next time! I plan to add more lights over the winter, so should be no problems next time.Comment
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Many if not most LED’s suitable for automotive or marine have reverse polarity protection, but I wouldn't always expect it to be present. It is also pretty easy to damage components being tested by powering them when only loosely connected through arching or shorting to ground. Only takes a few seconds to probe and label the wires before you disconnect them to make sure and even if you had to spend the money (looks like 3.99 in this case) it likely costs less to do so than possibly replacing even a single LED.Comment
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Jonsquatch,
I gather from your response, you feel my advice is poor? Do you know what a diode is and how it works? Simply put, a diode is a one way electrical valve. Its allows B+ to pass through one direction, but prevents it from passing through the other. So by its very design, it has the reverse polarity protection you speak of, but its certainly not an separate circuit that may or may not be added. An LED is nothing more then a diode (thats the "D" part in LED) with a lamp on one side of the diode. Wired with the polarity correct, B+ goes to the lamp and B- passes through the diode and the lamp illuminates. Wired with the polarity reversed, the B+ side of the lamp sees B- and the due to the diode, the B- side of the lamp sees nothing and the lamp doesnt illuminate.Comment
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I think your advice was excellent based on the information given, I was merely adding additional insight regarding the process I used for my recommendation.
You are absolutely correct the led will only light when connected with the correct polarity when it is forward-biased, when connected the wrong way only a small amount of current flows and it will not light and that is generally good enough when dealing with a 12 volt DC environment. LED's can be damaged if their a reverse breakdown voltage rating is exceeded, but that would typically be in a direct AC system, and most circuits are protected by placing a diode or additional LED's in inverse parallel.
Where I start to hedge my bets, however, is if you have a system in which an LED driver is used, particularly a low cost import unit, for example an RGB controller. It is significantly more like that damage will occur there in the driver circuit, especially if corners have been cut to save on production cost and the components in the driver circuit are not properly protected.
Not having all of the relevant information, not knowing who else might read any suggestions made, and attempting to limit the amount of extraneous detail that may cause confusion typically causes me to take the most cautious approach possible when I respond. I had initially started to give a more detailed description but I rewrote it a few times to keep it more general.
Keep up the good work!Comment
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