The day before yesterday I have bought a Sitecom USB to Serial cable (UC-104). The common problem with such cables is that there are no drivers from the producer for Mac OS X.
Usb To Serial Cable For Mac Download
The good thing is that most of these cables use a Prolific chip. Prolific is offering a driver for cables based on their chip on their site.
When I connected the Sitecom cable “About this Mac” reported that it is a Prolific but the driver did not load. I figured out that it is the Vendor Id and Product Id that were not matching. I had to edit /System/Library/Extentions/ProlificUsbSerial.kext/Info.plist and change the vendor and product Id’s apropriately.
(You can do that with every cable that has a prolific chip in it) And after that I had to run kextload /System/Library/Extentions/ProlificUsbSerial.kext. And imagine what was the biggest problem I had. Yes exactly that I forgot to run kextload.