Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 911 Technical Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Join Date: May 2011
Location: Rochester MN
Posts: 695
Garage
Speed sensor for Cruise Control

I have a long thread about my efforts to fix my non-working cruise control, but since I have narrowed things down, I felt I should start a new thread to ask a more specific question.

First - a little bit of background - I have verified the brake switch, clutch switch, stalk functions, the cruise module, and the actuator, all work.

The one test that never passed is the test that shows the speed signal. Most writeups say that as long as the speedometer is working, this is not likely to be the problem. But in my case, its the one thing that I have not been able to rule out.

So, does anyone have any tips on what to do next?

Specifically, the speedometer works, but there is no speed signal making it to the cruise wiring harness. I have done the test where you connect a multimeter to the appropriate pins and turn the rear wheels, and this test fails.

Here is other thread:

Clutch Switch for Cruise Control
__________________
1988 911 Carrera, M491 Cabriolet
Old 09-10-2018, 07:57 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
old man neri's Avatar
 
Join Date: Jul 2007
Location: Halifax, Canada
Posts: 1,196
I once had some very minor speedometer problems, it was reading correctly but it was a little slugish. I ended up cleaning the magnets on the transmission and it seemed to help. Just a thought.
Old 09-10-2018, 07:10 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
 
Join Date: Jul 2012
Location: GA
Posts: 795
I'd check the continuity of those wires in the cruise harness with a multimeter to rule out the wiring.
Old 09-11-2018, 06:39 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: May 2011
Location: Rochester MN
Posts: 695
Garage
Since my only solid lead on my non-working cruise is that the speed sensor signal is not reaching the cruise module, I thought I should remove the speedometer and see if there are any loose wires.

I didn't see anything loose, but perhaps someone can help by seeing if this looks right.





The wiring diagram I found said that a red/white wire goes from the speedometer to the cruise. From left to right, in the 5 positions, I have

Red/white
blank
red with a plastic connector
green
brown

I was a bit surprised that in the first position, there are 3 separate wires feeding into that one location.

Can anyone confirm if this all looks correct for a 1988?

Reminder: the speedometer and odometer work fine, I am trying to determine if there is a problem with the speed sensor signal output from the speedometer going into the cruise. I have already done the test to check the speed signal at the cruise wiring harness and that test failed, which led me to the speedometer.
__________________
1988 911 Carrera, M491 Cabriolet
Old 10-10-2018, 06:58 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
john walker's workshop's Avatar
 
Join Date: Mar 2001
Location: Marysville Wa.
Posts: 17,380
The A terminal should have the White with red trace wire.
__________________
8009 103rd pl ne Marysville Wa 98270
206 637 4071

Last edited by john walker's workshop; 10-11-2018 at 03:14 AM..
Old 10-10-2018, 08:20 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
Join Date: May 2011
Location: Rochester MN
Posts: 695
Garage
By A terminal, do you mean the one on the left in my photo? It has 3 wires, all of which appear to be white with red trace. I would assume that one of those leads to the cruise wiring receptacle.

Anyone know of a wiring diagram or marked photo, for a 1988 speedometer?
__________________
1988 911 Carrera, M491 Cabriolet

Last edited by megerian; 10-11-2018 at 03:17 PM..
Old 10-11-2018, 06:07 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
Join Date: May 2011
Location: Rochester MN
Posts: 695
Garage
Posting for comparison, this photo is not my car, its from a 1987 that I found in another thread.

They do not match my setup, which either means that 1987 and 1988 have different wiring, or that one of them is wrong, and given that my cruise is not getting a speed signal, I am hoping that mine is wrong.




In particular, this has a single wire going into the terminal marked with a + sign, where mine has 3 wires.
__________________
1988 911 Carrera, M491 Cabriolet
Old 10-11-2018, 07:12 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered User
 
Join Date: May 2011
Location: Rochester MN
Posts: 695
Garage
One conclusion I could draw, based on John Walker's comment, and the 2 photos, is that on my speedo, the red wire and the white wires are reversed. While that may explain the speed sensor output not reaching the cruise, would that make sense given that my speedometer is working correctly?
__________________
1988 911 Carrera, M491 Cabriolet
Old 10-11-2018, 02:18 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered User
 
old man neri's Avatar
 
Join Date: Jul 2007
Location: Halifax, Canada
Posts: 1,196
Here is the back of my 88 speedo. I think you have two connectors switched.


Last edited by old man neri; 10-11-2018 at 05:07 PM..
Old 10-11-2018, 05:05 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Registered User
 
Join Date: May 2011
Location: Rochester MN
Posts: 695
Garage
Well, that could not have gone any worse. Emboldened by the wiring diagrams, and the two photos, I decided to switch the two connectors (reversed the red with the white/red) turned on the car to try it out... snap! puff of smoke... fried the wiring!!!

I don't know if I also fried my speedo, or if I just need to rehab the fried wires and reconnect back to the way it was before. I also don't know why it happened, either due to my mistake of switching those connectors, or if by messing around with the wires and pushing the speedo back in I caused some wires to be crossed. CRAP!!!

Obviously I shouldnt have messed with it - given that I don't know exactly what I am doing, but after the switch, it did match exactly to the pic from Old Man Neri's post, and they are both 1988.
__________________
1988 911 Carrera, M491 Cabriolet
Old 10-12-2018, 02:31 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 04:00 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.