First off, I have the utter *wealth* of information on this board, to thank for this repair endeavour. If it weren't for you guys and your dedication, my poor 300D would have no cruise control for the rest of its life.

So.. here's the story. When I purchased the car (1984 Euro 300D), it had an aftermarket cruise control installed. The parts were all VDO, which was good.. but the thingie that connects to the speedometer, was a seperate box. Essentially, it was like this:

Trans -> Speedo cable -> VDO Box -> speedo cable -> Speedometer.

Since the short run of speedo cable snapped, I gave up trying to get this thing working again. That is until today, out of a sheer fit of boredom, I decided to remove the "little black box" from the back of a 240D instrument cluster, and hook the VDO box's wires up to it. It worked, sorta. The cruise surged back and forth, and couldn't lock on to a speed. One hour of re-soldering later, and viola! The thing actually holds a speed now. Granted, it does surge now and then (but very rarely, from the 10 minute drive I tested it with).. but accel-set, off, and resume all work now!

Which brings me to my problem. Decel-Set doesn't appear to do a thing . It doesn't turn the cruise off, and doesn't slow the car down. Is this in the cruise amp (Did I miss a solder point / break something?).. or more likely, the switch itself? If it's the switch.. how easy is it to remove? Thanks guys, you're the best!

Check out the troubleshooting procedure for the switch here:

http://www.gdl-online.com/testproc.html

If the switch is OK, it's probably the amp.

My cruise works great when its warm out (above about 70-75 degrees) worked great yesterday at 95F (I have no A/C ) Stalk functions all worked, and flawlessly, 0 surging or issues my whole 75 mile trip. However, whenever its cooler out, it either won't turn on, or it will surge constantly then turn back off. Solder connections? I re-soldered as much of the board as I could about 2 months ago, and it made a slight difference, but it still only works when warm. I've been thinking maybe I will find a small 12V heater blanket, and wrap it around the cruise box or something... I bet that'd work.... Whenever its colder out I could just flip on the "Cruise Heater" switch.

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