Need your wisdom on cruise control switch issue...
 

Howdy!

Thank you all for how freely you give your knowledge on this forum. I really appreciate it. Are there support groups for support groups?
But anyway, I'm having an issue with my cruise control. It won't hold a speed, and will only accelerate. I ran the entire battery of tests as described in the Bentley manual, but they were inconclusive. I'm suspecting that I have a situation similar to the ubiquitous headlight switch issue, where the contacts get tired and droop, and cause low and high beams to be on at all times. What I believe is happening is that the cancel function is sticking on, keeping the cruise control system from setting and holding a speed. I'm getting continuity between black and brown from the switch even when at rest. Shouldn't I only get continuity when it's engaged? Pardon me if this seems elementary, but I just want to confirm my logic.

http://forums.pelicanparts.com/uploa...1231220306.jpg

I made an insulator (a sliver of paper) between the black/brown contacts and took her for a spin. Now I don't even get accel when the lever is pushed up. ?????

Now I'm wondering if the diagram is way off the mark and the system NEEDS this connection to work...

Any rocket surgeons or brain scientists out there that want to contribute theories?

you should have continuity. when you cancel the switch it puts 12v at that terminal. what you have to do is remove the cpu behind the panel in the trunk. take the cover off. then, with a pencil type soldiering iron (advance auto $6.00) reheat all the solider joins on the bottom of the pc board. i used a magnifier lens while i sat on a stool and it took me about an hour to do it. take your time do every terminal. then your cruise will work.

kodioneill,

Thank you! I thought I was going crazy. I've got a 20 Gigawatt pistol type gun that gives me a sunburn when I use it. I'll have to dust it off!

Thanks again!

you need a low watt small pencil type with a very fine point. a high watt gun will ruin your components. as stated advance auto sells them for about $6.00.

kodioneill,

I see. I need a scalpel, not a Howitzer. I've got one of those pencil type irons also. Used it to repair my clock. It did work pretty well, now that I think of it.

Thanks again!!

Except on the Carrera's the cpu for the cruise is located right under the radio! Takes all of 3-5 minutes to remove.

Kurt,

Mine's located under the boot right next to the brake booster up towards the bulkhead.
When did they change the location?

Odd, maybe that was one of the changes for 1986, because mine is right under the radio.

CC not working
 

I have a 1980 911SC and I have been troubleshooting why my cruise control does not work for a while and still unable to determine why. I had the Cruise control brain tested by a shop-ok(Beckman) and I ran all the bentley tests-clutch switch, stalk,servo all seem to be ok. The only other test I have not ran is ohm reading between 11 and ground. Manual says to roll car and meter should deflect periodically (would this not be the same as me driving normally and the speedo reflecting my speed)? The only thing that stands out, is I should see a open between 6 and ground and I show 3.5 ohms. My brake lights work correctly. I am not sure if when I am doing the tests (I have the hood up and hood light is on) if this is causing a bad reading. Any help would be great as this is driving me crazy :)

Joe V -- On my SC, I had a bad Cruise brain that would only accelerate - nothing else. Swapped in a different brain and problem fixed.

The problem is with the brain. Needs a refurb via new soldering or professional refurb. They simply need refurb as most have not stood the test of time well.

I think location changed in 86 or post 86.

cruise control
 

I sent brain into Beckmans they tested and said it was fine. I sent it back and said rebuild it because it still did not work. Go figure

Crusise control
 

If someone has a defective cruise brain that will fit a 1980 911SC that works partially (IE accelerates, loses speed, anything know to work somewhat) and would not mind donating ( I will pay shipping). This would at least be a starting point and would allow me to confirm whether my brain is bad or not.

Thanks

For what it's worth, my 84 does the same thing only accel but then just deactivates. I have not had time to look at this yet. Seems to be a trend with these cars.

I have done work on the speedo in my 84 and the input signal to the speedo comes straight from the transducer on the tranny (via pin 32b on the speedo) but this signal is NOT the same one that goes to the cruise! The speedo conditions the transducer signal and produces a cleaner output signal on Terminal 'A' that feeds the cruise. So the speedo COULD work and yet not produce the signal on terminal 'A'.

Here's a picture from another project I did ignore the wires and special electronics.

http://forums.pelicanparts.com/uploa...1238685485.jpg

Sal I know you posted this sometime ago and may not remember all the details, but I have got a question. I have a 1980 911SC and cruise no work. I went thru the bentley manual and I believe all tests passed. Here in the lies the question, one of th PO's replaced the 85 mph speedo with a 150 mph is there any diff between the 2 odometers as far as connections?

I would need to look at the schematics to see if the cruise module gets it's speed signal from the speedo. It may very well be the case. I'll review the wiring for the 80 SC soon and report back. But in the mean time you could simply try disconnecting the Speedo and see if the cruise works? Just a thought.

What is the behavior of you cruise system? Not working at all? Sort of working, like not keeping speed but will set? Please provide more details.

In almost every case it's a bad solider join. Pull the ecu open it up then use a pinpoint solider iron to re solider the connections. I use a magnifier hood to see the connections. No need to use any solider just melt the existing join.

My brain has been tested and found to be good. The cruise is not working at all and has never worked from what I can tell everything checks out. In the wiring diagram it shows a connection going to the exterior lights and all exterior lights work correctly. Is it possible a reverse connection on exterior light and it still work casuing cc not to work? If you need more info let me know. Is there any way I can test each peice while it is in the car to verify what might be causing the problem. I have been working on this problem for years with no progress.

Thanks

After quick review of 81 SC schematic (don't have 80 schematics) I see the cruise module does indeed get it's speed signal from the 'A' terminal of the Speedo (just like the 84-89 cars). Terminal 'A' on the speedo is an output pin, meaning the speedo generates this signal. So, you may be onto something about changing from 85MPH to 150MPH speedo but I'm simply not sure and can't confirm if these 2 speedos do something different internally? You could try NH Speedo in CA and see if they could help answer this.