Down to business:
The eurorack system works on a +/- 12 volt system and uses either a 10 or 16 pin IDC connector system, here are some images courtesy of the Doepfer DIY pages
You can see here how there is -12v on the bottom two pins, 3 ground pairs of pins and the +12v pair of pins. This is the configuration for 95% of modules with the other 5% using the remaining pairs for bus access for gate and CV and an extra 5v for those modules that need extra juice. Please read the Doepfer Technical pages for further info.
The above image is the same for the modules and the standard bus access boards in most modular cases.
Please note that I will use "most" quite a bit as some manufacturers have strayed from this "standard", but hopefully from the info here you can work out any abnormality.
1. The first step you must make is identify what the configuration is for the bus boards in your modular case. Mostly the main manufacturers will follow the Doepfer standard having -12v on the bottom, but take a minute and check.
2. Second step is to identify on your module where -12v is on the PCB. This will usually be marked with -12v, "red stripe" or some other variation. If there is nothing there maybe post a question in this thread and someone will answer.
3. Third on the surface seems simple- match the bus boards to the module using the ribbon cable. In my experience this is where the big mistakes happen.
NEVER TRUST A RIBBON CABLE! NEVER TRUST THE RED STRIPE
Ribbon cables are not always built to a standard even though they are meant to be. You must always check the cables before connecting anything.
Go and grab a ribbon cable, have a close look at the header component. You should see a small triangle marked on one side. Now in an ideal world all the cables you have should have the red band of the cable matched up to this triangle, as this is the correct way to build them- using the red band and triangles as -12v, meaning when plugged into a bus board with keyed headers (black plastic things, not just pins like on the doepfer bus boards) the power is correctly aligned.
So when a module has "red stripe" on the PCB it is assumed that it is referencing the -12v.
In my short time of euro-accumulating I have had cables built with one end having the red stripe matched to the triangle and the other end not- boom kapow hiss, instant voltage reversal, and other cables built perfectly backwards, with both triangles not aligned to the red stripe. This is kinda ok if you don't have keyed headers, but if you do have keyed headers and you have to twist the cable to plug it in- boom, kapow, hiss yr module is fried. SO again:
NEVER TRUST A RIBBON CABLE! NEVER TRUST THE RED STRIPE
So after step 3 you will have identified the + and - power from yr busboards, identified the + and - on your module, have checked the ribbon cable's construction to ensure the red stripe is the same both ends- ideally matching the small triangle- you can now plug it in
The only modules I haven't had experience with are Cwejman, and I know there is something funny with those, so if someone can chime in, but by following this procedure for every module I've bought either new or second-hand I've never fried a module (fingers crossed).
I'll try and add some more pics to this, espeically of the cables, plus I'll show you an easy way to reclaim a improperly built ribbon cable. But this should get you a little further to sonic joy.
