Tempomat (cruise) w124

[larsko]

Can somebody enlighten me on the black "code plug" on the back of the cruise control unit? As far as I understand, the control unit (the big silver box) is shared across various models, whereas the black plug is more model specific (the older control units don't have a code plug on the back).

For my car (1989 230CE unusual in the us, I know) there is a number of control units available (A0235452132 A0165457732 A0145454032 A0055450532) but there is only one code plug (007 545 0632) and it is hard to find, i.e. expensive.

I have the usual problem. Cruise engages sometimes, holds for a while, but cuts out eventually. Sometimes it does not work at all.

I know bad soldering in the control unit is a common problem. Could it also be the control plug, or could I reasonably think the plug is ok and order a correct control unit with a different plug and reuse my old plug?

Thought?