Just wanted to mention that most manufacturers do not use universal connection to the front panel LEDs/Switches.
For example to reuse HP, Dell, and Compaq OEM cases with replacement motherboards, I had to cut the front panel wiring harness out of some old 486 and pentium 1 cases that I had that were universal, then I had to cut the single black plug off the HP, Dell, or Compaq harness, then trace the wires back to what they went to, and then match up the 2-pin connectors with the wire pairs and connect and shrink tube them, and then the OEM case was then converted to a universal wire harness from that of a wiring harness for the front panel that only worked with the original motherboard the manufacture installed in the computer since the pin outs can change between manufacturers of motherboards.
If you dont have a universal wire harness to cut out to use in an OEM case the other 2 options are either, carefully remove the wires from the single connection from the original OEM harness and rewire it to match up to the new motherboard. * This however requires a small tool shich can be either a push pin or a safety pin to carefully unlock each of the pins from the connector. The connector has small black tabs that the pins lock into , and tugging the wires out of the connector without unlocking them from the retaining locks will damage the small metal wing on the pins that lock the pins into the connector.
The other method if you cant unlock the pins and rearrange them in the original single connection is to cut the wires with plenty of length left to mix move the wired devices from the front panel to match up to the correct motherboard pins, but this is a very sloppy way of doing this.
Lastly these 2 alternate methods without converting it to universal means that down the road if you go to swap the otherboard out again, you will have to repin or rewire it all over again, so converting the OEM case to universal 2 pin connectors is the best way to go.
I have 2 systems at home that are OEM cases converted to universal harness. A Compaq Presario S6030NX which has gone through 2 motherboards since 2003, original Athlon XP 2800+ died in 2006, then I placed a Pentium 4 into it for a while until I got a deal on a dual-core CPU & motherboard for $65 in 2009 and its still running on that 5 yr old motherboard. The other was acquired recently a HP A1210n that was getting thrown away because it would lock up tight and it had the bad capacitors in it all swollen and leaking, and I liked that full height case and so I converted it to universal and installed a $43 brand new Biostar Socket AM3 motherboard into it with Athlon II x2 215 2700Mhz with 2GB of DDR3 1333mhz, and added a GeForce GT430 video card that I got for $25.
The easiest route to go for anyone is to just buy a new cheap case and install to that. Sometimes I go this route, but if I have an OEM case that I like the features and appearance of, I will go through the 30 minutes to 1 hour it takes to universalize a non-universal case.
* Other areas you can run into problems with OEM cases are just like BC stated where the board doesnt line up with the backplate I/O shield etc.
I have also had to drill out mounting holes to convert the power supply bay to take a universal power supply because HP/Compaq decided that they wanted to use different mounting orientation to their power supplies that otherwise share the same dimensions of that of a off the shelf 500 watt power supply, but only 1 of 4 holes on the case line up with the universal power supply. After making a rubbing template of the proper universal mounting and carefully drilling the case out without anything inside for metal filings to get down into, and then blowing case out with compressed air to get rid of any metal fragments, I then was able to install an off the shelf power supply and fully universalize an OEM case.
Lastly with this being a BIG WARNING, is that some manufacturers have the mounting base of their cases very similar to that of a standard mATX or ATX case, yet there is an extra dome or stand off that does not line up with a replacement motherboard. If you do not catch this when you install a new motherboard you can fry your new motherboard by shorting component legs to chasis ground. On reuse of OEM Cases, always double check that each stand off or mounting dome matches to a mounting hole in the motherboard you are putting into the case. Sometimes there will be an extra and it can spell disaster if powered and board is shorted. Stand offs are easier to deal with, just remove them, however if its a formed mounting plate with domes drilled at their tops, you will have to flatten (hammer) the dome down so that it does not make contact with the motherboard. I found that a socket on a 6" socket extension with a hammer to drive the socket face directly into the dome top works best to gain access to the area without risk of striking other parts of case with hammer etc. * Be sure no components are in the case while you do this, especially the hard drive!!! I almost fried a motherboard once due to this. Fortunately the powersupply when powered was making a ticking noise and so I knew there was a problem and shut it off to look for the short. When found and problem resolved the system turned on with no problems, and that was with a 486 installed into a 286 case many years ago, however I have seen the problem more recently such as in the HP A1210n case which had a dome that needed to get flattened which did not match up to standard ATX or mATX boards.
These lengths of reuse many people will not bother with and they will just spend the $15 - $30 for a new cheap case for mATX or ATX without Power Supply to mount their parts into.
