Chris and "spkenyuk" Maserati 3200GT August,year 2000
Has SD2 electronics.
The modules are: Nokia Type HF-5 (OW3HF-5) The module which caused the trouble is unbranded,dated 9/06 with a serial #6101086. It appears to be a signal receiver since it has a short wire aerial. Has a power supply & a twenty-pin outlet. Trust this helps.
The nokia bit of kit is from a HF5 handsfree system. There would have been at least 2 other leads / modules that would have plugged into that when it was fully installed. Small red plastic block with 2 iso pass through connectors for the stereo so that sound from phone calls would come out of the car speakers.
You then would have had one or both connections for a powered phone craddle and or a wired remote for phone functions.
The 2nd module you have with a serial #6101086 . The only thing i can think of that would fit your description is either some sort of keyless entry that has been added or bluetooth streaming device that has either been taped into the phone system or stereo at some point.
I cant see any reason why any of those apart from possibly a keyless entry system would be able to cause rogue CEL light /codes.
If you have or can get a picture of the unbranded module will see if i recognise it or anybody else does.