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Join Date: Aug 2004
Location: Madison, WI
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Speedometer and cruise just flicked off

Dang, my speedometer and cruise control just died on the interstate in my 1993 C2 Cabriolet 964. Both worked for a few minutes and then dropped out again for good. No warning lights or any other issues to report. I searched and found that possibly the VSS -Vehicle Speed Sensor 96460621001 is a possible culprit for the speedo, but found nothing of the speedo\cruise combo failure. Also, I did just have the face of my speedo replaced over the winter. I put on a couple of hundred miles with no issues after the speedo install, but you never know. Does the speedo report back to the cruise? Any one have any thoughts? How hard is it to replace the VSS? Speedo repair is easy.
Thanks in advance!

DonS
Old 06-08-2017, 08:46 AM
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do you know someone with a similar car? maybe pull and swap the speedos over just to eliminate if the issue is in the speedo unit itself first...
Old 06-18-2017, 03:13 PM
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Getting better. I tried a different ABS Relay, Frequency Converter and even soldered the bad looking joints on the speedo. Now the speedo works, but the spoiler light is always on. I did not test the spoiler for automatic deployment at speed, but it does raise and lower manually. I suspect the problem lies in the speedo. Time to crack it open and check solder joints. Maybe a pro can repair it.
Old 07-31-2017, 11:54 AM
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I have always had 100% satisfaction from North Hollywood Speedometer.
Old 08-22-2017, 07:35 AM
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I just had the same problem. Capacitors on the speedo board went bad and let the smoke out.

These caps are getting to the age where failure can be expected.

I sent it to Corey Shepherd at Specialty Gauge and he fixed the board, the face, and the odo gears which were close to the end of their service life. Including postage time it was a week, and could have been less time if I didn't miss his call.

Wasn't cheap, but considering everything that was done, I'd say fairly priced. The speedo gauge face was pretty ugly with the lights on, and I wanted to get that fixed anyway.
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Last edited by 914986; 08-23-2017 at 07:22 PM..
Old 08-23-2017, 07:20 PM
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I thought the speed situation was fixed, but it reared its ugly head again. Makes no difference what ABS Relay or Frequency Converter are installed, the speedo and cruise just randomly quit. The odometer stops as well. I think I'll ship it off this winter to have it repaired. I suspect this all started when I sent the speedo in for replacement of the face that started to flake...
Old 08-28-2017, 11:22 AM
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Ship it to the manufactory for this
Old 08-28-2017, 08:17 PM
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Palo Alto Speedometer found no real issue, but we decided to replace the chip and capacitors. Problem solved!! They even improved the MPH calibration - spot on with GPS now! Cost was $250, but shipping each way was around $20 - so $290 total out of pocket.

Now I am back to chasing an intermittent idle issue and cleaning leather.

Thanks for all your help!!
Old 11-26-2017, 09:34 AM
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Idle issue could be a vacuum leak.
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'91 964 Targa guards red, cashmere
several 914's and loads of parts
Old 11-29-2017, 06:27 PM
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I had a similar issue... my speedo was ok I think.. but the cruise control just stopped functioning..
Turned out to be my clock with bad solder joints on the back...
Old 11-30-2017, 01:16 AM
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I had problems with headlights, cruise, replacing the ignition switch solved my issue.
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Ralph W
Old 11-30-2017, 06:59 AM
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Problem not solved. After a long winter break, and a long drive to warm up - the cruise, speedo, odometer and all speed related items failed just as before. It works normally when cold - I never see the problem during short haunts around town on our cool spring days... I need to check where the speed signal goes - cruise servo, cruise computer, clock, speedo, main computer and start repairing\replacing. And I need to drive it hard to get it to fail making testing a crap shoot. Dammit!!

PS: this is a repeat as on Rennlist as I need all the help I can get.

Last edited by Don Settergren; 05-08-2018 at 06:23 AM..
Old 05-08-2018, 06:18 AM
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I just sat down with the wiring diagrams. That little white\red speed signal wire goes to:

Alarm Control Locking Control Unit
Rear Spoiler Control Unit
Auto Trans Solenoid Lever Lock Control Unit (my car has a stick)
Convertible Top Control Unit
Control AC Heater Control Unit
Cruise Control Control Unit
Speedometer
Central Informer
Rev Counter With On-Board Unit
Central Electric

I don't see the speed signal wire going to ABS as ABS is self contained with each wheel speed sensor as far as I can tell.

I am still not sure where to start for my next step. Either the signal is lost at the source or somewhere in the above list it is shorted causing my troubles.

Oh and, wiring always has two sides. Gotta chase down the other side next...
Old 10-07-2018, 03:35 PM
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Hmm, the ground wire next to the Cruise Control Control Unit is crusty. I could see in a cab like mine or a coupe with the window down during rain that this ground could get corroded. Maybe I'll replace the control unit and clean the ground - one at a time of course.
Old 10-07-2018, 03:55 PM
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