Cruise Control & Brake Dilemma
 

Re: 1987 560 SL

The cruise functions normally at all functions when operated by the control lever on the steering column. As soon as you touch the brakes with cruise engaged, the unit is somehow "reset" and becomes inoperative until the car (ignition) is turned off and restarted, at which time the cruise is functional again until...

I was advised that the brake lights can be voltage culprits causing some flucuation that triggers a problem such as this. I switched brake and back up light bulbs (as the latter filaments looked to be brand new in comparison) with no success. The concept of some electrical gremlin in the brake circuit makes sense based on the pattern of failure, however. Any other suggestions for the next step in troubleshooting?

Thanks.
Mark

is the bulb brass based or nickel? switch to the OEM nickle colored ones...

Check here on bulbs: http://gdl-online.com/bulb.html
The problem is on the reset circuit from ground(pin #8 on CC amp.); I'm not clever enough to figure out the circuit, but bulbs will NOT do it most likely (see above link). Several folks, including me, have posted the same dilemma with no resolution except getting a rebuilt amp. from GDL. I'd check and clean the stop light microswitch at the brake pedal. Some folks resolder the amp. circuit board, hoping to correct a cold solder joint. As always capacitors are suspect and 15 year old chips don't build confidence either.

If some EE type knows what a simple reset circuit looks like, I'll try some selective component replacement on my amp.

Please post outcome on your solution (hopefully).