'82 911SC Speed Signal/Rostra Cruise Control

[jaustinmd]

I have an '82 911 SC with a 964 dash and gauges. I've considering installing a Rostra cruise control system - I know there are reports on this forum of successful installations with good performance.

As I understand it, the speed signal sensor outputs the signal from the transmission via a brown/red wire to the speedometer. On the original speedo, there was a terminal to output the signal to the cruise. On the 964 speedo, I "think" the speed signal output from the speedo is the red/white wire.

Kris Rose, who repairs the OEM cruise modules, told me he uses the exact same signal to test 911SC and 964 cruise modules, so the signal obviously is the same coming from either speedo.

Does anyone happen to know these technical details for setting the module's dip switches:

(1) Do you know if the speed signal from the transmission (brown/red wire) has a sine wave or square wave signal?
(2) Do you know the number of Pulses Per Mile ?
(3) Are the outputs from the speedos just a pass-through signal and exactly the same signal as the red/brown input wire or is it different in wave form or Pulses Per Mile, etc.?

Of course, if anyone has done a Rostra 250-1223 installation and has all the dip switch settings for a successful installation in a 911SC or 964, that would be most helpful!

I'm interested in getting the technical information and not a debate as to the whether to even have a cruise control in a 911 ... some of us do HAVE to drive on the Interstate occasionally! Ha!

[Uwon]

John, did you ever find the answers to your questions? If so can you share as I need to test my speedo.
Cheers,
Johan

[jaustinmd]

Originally Posted by Uwon

John, did you ever find the answers to your questions? If so can you share as I need to test my speedo.
Cheers,
Johan

The speed signal is a square wave signal.

There are 8 magnets on the sensor mechanism, so I found a calculator on the internet where you can take your tire size and figure how many revolutions it makes in a mile. Multiply the number of revolutions per mile X 8 and that's the pulses per mile - mine came out a little over 6400 PPM. The Rostra had a "6400" range and it worked perfectly.

I never did get an answer about whether the 964 speedo passes-through the "raw" signal or not. However, I jumpered the "raw" signal from the sensor (red/brown wire) to the Rostra's speed signal input and it worked perfectly (and my speedo still works!).

I'm very pleased with the entire Rostra cruise control system!