I have been farting around trying to get my cruise control on my 85 300D to work. I replaced the underhood actuator, cleaned the wire terminals under the hood, pulled out the cruise amp, cleaned the terminals, pulled out the circuit board (did not see any bad solder joints or burned area).

Cruise does not work BUT..........today I hit the set/accel and the car started to accelerate!!! Soon as I let off the accel the car would not hold speed.

Any ideas?

Does anyone in the Houston area have a known good cruise amp I could try?

Thanks for any info!!

__________________
Anything is possible if you don't know what you are talking about........

1985 Mercedes 300D
2007 Mercedes C-350
1980 Mazda Rx-7 (SA22C)
2005 Jaguar XJR
2007 Jeep Wrangler

Even if the amplifier does not seem to have any bad connections (cold solder joints), resoldering the board may fix the problem. Many here, including myself 2X, have fixed cruise problems by resoldering.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Cruise amp, and no, I don't have a good one either.
I do however have several bad ones and a soldering
gun.............

If you need/want to resolder your old one, you can borrow it

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81 Mercedes 300SD 289k.......SOLD
82 Mercedes 300CD 252k......slow ride

82 mercedes 300 SD...mi Unknown
83 Mercedes 300D ????ksniff..gone too
84 Mercedes 300D 148k........SOLD
85 Mercedes 300TD 386k and holding some one elses project

Thanks, I do have a soldering iron. I soldered my ACC this weekend and now it is NOT possessed.

The cruise amp looks like it would be a nightmare to re-solder! I wanted to try a known good one. Then I will probably kust buy a rebuilt cruise amp.

__________________
Anything is possible if you don't know what you are talking about........

1985 Mercedes 300D
2007 Mercedes C-350
1980 Mazda Rx-7 (SA22C)
2005 Jaguar XJR
2007 Jeep Wrangler

I just did this over the weekend and it took me about 15 minutes from start to finish. Cruse works perfectly now, and prior to the soldering I had the EXACT same symptoms as you.

Just try it, it'll work and it wont take too much time at all. In fact it took me longer to remove and replace the thing then it did to solder! I hate having long arms sometimes

Mine looks like it had some clear coated shwack all over the board. Did you have to remove this stuff? Also do you have the amp with IC chips or the older analog system?

__________________
Anything is possible if you don't know what you are talking about........

1985 Mercedes 300D
2007 Mercedes C-350
1980 Mazda Rx-7 (SA22C)
2005 Jaguar XJR
2007 Jeep Wrangler