In all american 91 to 93 129's the 1432 was standard equiptment. There are two possible problems one is that you have the wrong code as we have seen ( check the serial # on the chassis of the head unit in the dashboard. If upon verifying the code and it is right but still doesn't respond then the code board in the radio is probably out. Check in with Cleeve in my repair shop at
www.mercedesradiorepair.net and he can help you out...
Scott