87 300TD Cruise Amplifier
 

I am having a problem replacing the cruise amplifier on my 87 300TDT. I know that the amp was the problem because I could swap it with a working one and the cruise worked. I bought a replacement from an online vendor and there is a second set of pins on the back of the new unit. This appears to be for a reference resistor as far as I can tell from shematics available on the Mercedes CD manual. The new unit does not work at all as it is. So I would like to know if I just have got the wrong amplifier for my car, or whether the unit has been 'updated' and I will have to make some changes in order to make it work. If anyone knows the answer or has solved the problem I would love to hear from you.

Cheers,

Chris

P.S. I tried playing with removing pin 14 from the plug, as suggested in the manual - but this did not help at all.