Re: [MBZ] 300D cruise control troubleshooting

[Peter Frederick]

All of the electronic control (vs the vacuum type used earlier) ground 
through the stop lamp bulbs.  Sounds kinda nuts, but what happens is 
that when the lamps light up, there is suddenly 12V on the ground side, 
and the amplifier drops off line.  If you don't have good, or matched, 
lamps, you can have problems with the CC amplifier.  Usually it just 
won't set, but sometimes it's erratic -- won't hold speed, etc.

On the Volvo, mismatched bulbs, even if brand new, will cause the lamp 
out warning light to come on.

Peter