notny41

(revised)

Hey everyone, just bought a 1986 944 Turbo that has had a few wiring modifications to it. The cruise control does not work on it.

I have taken the solenoid apart and cleaned the wipers up on it. Everything inside there looked good too. I purchased another CC brain box and put that in and still no cruise.

The 8-conductor plug seems to be the inputs to the cruise control and the 7-conductor connector seems to be wires that all go to the solenoid.

So on the plug that has 8 wires going to it:

1 - Red/Black - speedo input
2 - Red/White - Brake input
3 - Brown/Yellow - Stalk pulled back
4 - Grey - 12 +
5 - Blue - Stalk pulled down
6 - Yellow - Stalk pushed forward
7 - Brown/White - Clutch input
8 - Brown - Ground 12v+

notny41

Ok, first of all, I got my cruise control working, which is an amazing feeling since the previous owner said it had never worked for as long has he has had the car either. I LOVE my cruise control. It works fantasticly - no surging, no 10 mph over what I set it at, just solid immediate cruise control.

I purchased a Haynes manual for the 944 (including Turbo) specifically so I could find out how to correctly test each of the cruise control components. After days of anxious anticipation the Haynes shop manual came. I flipped to the back where the index was. Found "Cruise Control" and which page it was on. Quickly flipped to that page only to be informed that there are no instructions for the cruise - instead it says to bring it to a shop for this... I can't tell you how disappointed I was in Haynes.

So in the absence of having the correct procedures for testing my components I did some internet searching and found a youtube video that showed a guy taking his servo apart and cleaning the slider (potentiometer) contacts inside it. So I took mine apart and could see the circuit board and which contacts went where inside there (motor, clutch, potentiometer). I also found a diagram that confirmed my theory on these wires and their functions. Basically how the servo wires break down is:

blue (#8 pin) is motor -
black (#7 pin) is motor +

red (#4 pin) is potentiometer +
yellow (#3 pin) is potentiometer slip contact

white (#6 pin) is brake light

green (#5 pin) is the electromagnet that engages the motor to the gears
brown (#2 pin) is the ground

there is no #1 pin

So I got a little 12v motorcycle battery and decided to test the motor and the electromagnet. when I jumped from the battery to the 7 and 8 pins, I could see the motor spinning. When I jumped from the battery to the 2 and 5 pins the electromagnet engaged and pulled the gear mechanism down to meet the gear on the motor. Then I put a multimeter set on ohms on pins 3 and 2 and moved the slider gear by hand I could see the ohms steadily increase and decrease depending upon which way the gear was moved. When I left the meter hooked up and held the electromagnet down by hand and applied voltage to the motor I could see the ohms change as the motor drove the gear. So I figured the servo unit was fine at that point.

Then I saw a video where a guy got his cruise working by finding some cracked solder joints on his ecu. So I took my ecu off and took it apart. I didn't see any cracked solder joints, but based on another post decided to look at the capacitors. Apparently the caps are another thing that go bad on these. I de-soldered the capacitors that were on the unit and put some new ones on it. Tried the cruise and still nothing.

So then I ordered a used ecu off ebay and when it arrived I tried it and also nothing. So I was beginning to wonder if I had some wiring issues with the car - especially since I did spot a couple of splices into the cruise wiring which had me a bit worried.

At that point I searched the web and found the official porsche shop manuals available in digital format for free. So I downloaded them and in those three sets of huge zipped up files were the official test procedures for testing the wiring. I did all of the tests (test for power, brake switch, clutch switch, cruise control switch, speedometer) and they all tested out fine - and if that is the case then the manual says to replace the ECU unit.

So at that point I remember one post or video that said they fixed their cruise by just re-soldering all of the connections on that ECU. (Similar to the one that said to check for cracked solder joints) so since I couldn't see any cracked solder joints and I had time on my hands one night I decided to get the old soldering iron out and just start re-soldering every contact on that ECU board.

Wouldn't you know it, that when I installed the ECU back into the car and took it for a spin that cruise control, which had not worked in years, was working perfectly again.

So - here's my advice to anyone tracing down a cruise control problem. Do the tests first on the servo because they are easy. If those all check out fine, then resolder every connection on that ECU board - and maybe replace the capacitors if yours look like they are starting to bulge at the top. (sorry - forgot to take pictures of the ECU)

gruhsy

Nice write up. Nice to hear you got it working. Funny the plastic gear in the third pic down looks like the sunroof gears.

ttAmerica RoadsterAWD

Nice! Welcome to the board! Thank you for taking the time to post your thoughts and approach, will help me in the near future as I also have a CC issue.....It doesn't work! Thank you for your contribution

Jaime

notny41

Let me know if you have any questions along the way - I learned a lot while working on mine.

You will get it going, I have no doubt - they are pretty simple systems that don't interact with the central computer or anything like that.