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If you have bought a nice new computer case and you are trying to wire up the front panel, trying to work out which of the LED wires are positive or negative can be a puzzle as there never seem to be any instructions...

Motherboard Case Front Panel connector wiring

Motherboards and system cases vary. Your motherboard may not have all the items I mention here, and the same holds true for your case. Furthermore, you may find that your case and motherboard don't match in every situation; for example, some cases have a turbo button and some do not, and some motherboards have a connection for a turbo button and some don't.

IWatch out for "off by one" errors when attaching cables to pin headers. In particular, some motherboards combine several pin connectors into a larger block. The individual connections are the same, the motherboard just physically groups the pins together into a larger matrix. Be careful when working with these as making a mistake is much easier to do. Refer to the manual. the system is in a tower case, it is much easier to perform this procedure with the case resting on its side.

LED's have two wires and are unidirectional, so they will not work if attached backwards. You need to connect the positive lead from the case to the positive pin on the motherboard, and the same with the negative. Unfortunately, the case connector almost never has the positive and negative labelled.

Case Wiring Positive and Negative

Fortunately, attaching them backwards will usually not cause any damage; the LED just won't work. One tip you can use for most cases, is that each LED has one coloured wire (green, yellow, red, orange, blue) and another wire that is either black or white. When this is the case, usually the coloured wire is positive (signal) and the black or white wire is negative (ground). This isn't always true, but it's better than a random guess in most cases.

Test your front panel LED first to see which way round the coloured wire is, is it positive or negative? Once you establish this write it down on a little label and stick it inside the case somewhere.

If you need to buy the little plastic ends for the connectors for some reason then you might try a Maplins electronics shop.

Personally, I always cut off connectors from discarded cases and save them in a box somewhere, coz you never know when you might need some!