No adapter necessary - just use the red/brown wire going to the speedo from the VSS sensor.

John

vacuum servo removal
 

Plan B
Here are the Rostra Universal installation instructions:

http://www.rostra.com/manuals/250-1223Form4565G.pdf

the servo mounting fixture is underneath the servo, and hidden from view. It's made of stamped steel, and held in place by two 10mm bolts. The servo can be pushed up to allow access to the bolts--plan on taking your time--small hands help a lot. I removed the small vacuum hose at the white T to get to it.

Update--FYI, access to the servo mounts and dip switches are much easier if one removes the engine compartment blower--I should have done that to start with.


http://forums.pelicanparts.com/uploa...1482532860.jpg


http://forums.pelicanparts.com/uploa...1482533012.jpg

Old servo out, and new bracket installed--time lapse, about 2 hrs. Bracket bent to horseshoe shape--comes flat--access to the servo mounts and dip switches are much easier if one removes the engine compartment blower--I should have done that to start with.

I'm leaving hoses and wiring in place in case someone wishes to reconnect old system. Large vacuum hose will need to be plugged.

http://forums.pelicanparts.com/uploa...1482538730.jpg

next: fasten new servo, plug hoses, attach cable to accelerator, run wiring.
I suspect the wireless switch will be a good choice, given the lack of room under dash for more wiring, and my lack of patience--leaving original CC lever in place.


UPDATE--11 Jan

"One can learn through experience, but often the tuition is very high"
.......Brorag (ask me how I know)

to wit................
Prior to installing new servo, BE SURE to confirm switch settings are per your car's requirements. Because of it's final location, the servo is practically inaccessible after installation and the switches are recessed into the servo about 3/4" and cannot be seen or accessed. After de-mounting the servo so I could see the dip switches, I used jaustinmd's configuration listed in his install at the beginning of this thread. Pay special attention to dip switch #12, setting it to match the control switch (open or closed circuit) you've chosen. This piece of dumb tax cost another 2 hrs. FYI, access to the servo mounts and dip switches are much easier if one removes the engine compartment blower--I should have done that to start with.

http://forums.pelicanparts.com/uploa...1484165020.jpg

http://forums.pelicanparts.com/uploa...1484165035.jpg


http://forums.pelicanparts.com/uploa...1484165050.jpg

http://forums.pelicanparts.com/uploa...1484165069.jpg

wire routing
 

....after spending a morning looking for an existing factory path through the firewall, I gave up and expanded a previous hole drilled for satellite radio antenna close to the top of the back seat, and routing the harness under the carpeting along the right of the drivers seat. The wire to the right is the alarm system. The car is a cabriolet, so there is a panel covering the area shown. Had to extend harness 5 feet. Will protect the harness with cover included with the kit.

Wiper switch replaced. Wayne's tech articles helped a lot.

the stuff in this message took about 5 hrs.

http://forums.pelicanparts.com/uploa...1483033533.jpg

grommet installed later.

wiring harness run under rear carpet, then through left passenger seat channel--other wires there also, so apparently OK.

http://forums.pelicanparts.com/uploa...1483140104.jpg

...yes, I need to clean the leather--also had to clean out mice hotel behind the passenger foot rest--commie rat bastards.

Universal kit calls for a t-bar adapter for my set-up--note vacuum hose to plug from old cruise control module:

http://forums.pelicanparts.com/uploa...1483140271.jpg

does not come with kit--arrives 2 Jan..
Amazon Prime--Rostra T-Bar Adapter 2.5L EFI Engine - Part # 250-4184
Sold by: Wraith&Co
$7.99

...will work the connections under dash next while waiting on adapter--time spent 2 hrs--complicated by having to re-light cigar several times...

cigar marinating till next time.....
http://forums.pelicanparts.com/uploa...1483140314.jpg

final connections in engine compartment
 

the T-bar assy arrived and I installed as shown here--it has a termination at it's distal end that looks like this. The distal end of the controller cable has a similar termination.

http://forums.pelicanparts.com/uploa...1483392050.png


I had to widen the slot where the t-bar connects the the throttle slightly to accommodate the distal end of the T-bar adapter to allow the terminated end of the t-bar cable through the slot.


http://forums.pelicanparts.com/uploa...1483392234.jpg

Take the lock washer nut provided in the kit and form a thread into the distal end of the controller cable by using your fingers.
After getting it started, use a small wrench to continue forming a thread about 1 3/8" long.

Screw the formed threads into the snap-in adapter provided in the kit--do not install the adapter into the original controller cable bracket yet.
Connect the two cables using a chain connector and a connector cover provided in the kit. The connector will look something like this--the cover is a 3/8"piece of plastic tubing:

http://forums.pelicanparts.com/uploa...1483392771.jpg

use the cover to close the slots in the connector.

Screw the Snap-in adapter onto the distal end of the controller cable. Adjust the length of the cable assy using the threaded adapter so that there is a slight amount of slack in the cable length when you hold the snap-in adapter at the original controller cable bracket.

Snap adapter into the original controller cable bracket. The assembly will look like this (minus the chewed up plastic wing--I had snapped the adapter in before I should have and had to remove it to do the above connections)

http://forums.pelicanparts.com/uploa...1483393585.jpg

There are two or three wires from the controller that need to be addressed at this point:
--The black ground wire must be connected to a chassis ground--there is one just forward of the fuel filter and a pain-in-the-butt-to get to. I used the one connected to the engine lid hinge.
--There is a dark blue tachometer wire that is used to disengage the cruise system on cars with automatic transmissions. It would be attached at the connector for the old cruise computer.
--On cars with a straight shift, that wire is grounded. If your car is a straight shift, I would suggest separating it from the harness prior to running the harness through the firewall, and grounding it with the other ground wire discussed above.

There is also a connector used when a separate VSS is used instead of the original one feeding the speed signal to the speedometer, and is labelled as such--leave it unattached and plan to use the original VSS wire feeding the speedo.

time spent--about 2 hrs and 1 1/2 cigars. Time for a martini...

best pic showing connectors.

http://forums.pelicanparts.com/uploa...1483395756.jpg

under dash wiring
 

....started under dash wiring--lessons learned:
1--If you find that you need to remove the speedo, make sure you have a good pic of the wire placement prior to removing them. Mine had broken gears, so it was removed to send out for repair. Should you pull a Brorag (me) and not properly record the connector positions, there is help. There are several iterations of speedos, using different color wiring connectors. After about 1.5 hrs of research, I found my setup. Many people have been down this path, and have posted pics on Pelican. Here's mine:

http://forums.pelicanparts.com/uploa...1483479635.jpg

note--I later cranked engine and tach worked.

update--11 Jan 17--odometer now working after repair.

2--I was thinking I would connect the original VSS sensor wires at the speedo--that was a mistake. You can see the black/brown VSS sensor wire in the above pic.

The best place for the connection is by tapping the other end of the black/brown wire (on my car) at the connector for the old cruise computer under the dash. The diagram by jaustinmd at the beginning of this thread is your best source.

Connect the grey wire on the new wiring harness to the black/brown wire coming off the old cruise computer under the dash.
I connected the two red and purple brake wires the same way, through the harness, using the cruse control electrical diagrams in the Bentley service manual (pp 970-61), which provides wire color and connector pin locations.

http://forums.pelicanparts.com/uploa...1483568321.jpg

There is a dark blue tachometer wire that is used to disengage the cruise system on cars with automatic transmissions. It would also be attached at the connector for the old cruise computer. My car is a straight drive, so that wire is grounded. I would suggest separating it from the harness prior to running the harness through the firewall, and ground it with the other ground wire. (repeat)


http://forums.pelicanparts.com/uploa...1483480737.jpg

this took 3.5 hr, including research....getting too old for this--martini time. Getting close.

Wouldn't it been a lot easier to just call Pelican Parts and ask them to locate you a very reliable
rebuilt OEM cruise control ECU?

next thing to sort out.
Q: Do I need to connect the Dark Blue Tachometer (TACH) or Light Green Neutral Safety (NSS) wires from the Global Cruise system's main wiring harness for cruise control operation?
A: While neither the Tachometer Signal wire (for manual transmission vehicles) or Neutral Safety wire (for automatic transmission vehicles) need to be connected for cruise control operation, we highly advise that they are as they provide over-rev protection by disengaging the cruise control system in situations where the engine could be accidentally "knocked" into neutral while driving (NSS/automatic transmission), or when the clutch pedal is depressed (TACH/manual transmission).

update: Rostra Tech--"ground dark blue wire, and tape off light green wire."

Dave, I've been there, did that.
When I rebuilt this car a while back, I sent the Cruise brain out to a reputable repair house here on the east coast. I had it out today and the rebuild date was 2011.
Unfortunately, the early analog units MTBF is high, due to their analog design and age of the boards (many of the components, solder joints and traces are failing). Porsche went to the digital unit in 1988, and that unit had been a big improvement.
Current digital technology is an improvement over Porsche's digital design, and the unit I'm using is commonly installed as OEM on new cars.
I like doing cross country in addition to the local mountains, and have found a reliable cruise unit worth it. If I were doing strict restoration, I might reconsider the old unit, but that's not my goal. I am, however, keeping the OE parts and wiring, much of it insitu, should the next owner wish to backdate it.

Given its short life, the rebuilder doesn't sound very "reputable".
Did you ever call Pelican Parts about their recommendation for having the unit rebuilt?

Re-assy and test next.

Road test: Unit works as advertised on a 7 mile test run. Semi-finished wireless control location--will center between gauges.

Next, put this thing back together, clean it up and drive it--round trip to outer banks coming in a week.

http://forums.pelicanparts.com/uploa...1484174210.jpg


http://forums.pelicanparts.com/uploa...1484174381.jpg

note gal of corn removed from between firewall and engine insulating pad--for those interested in the rest of the story, go here: http://forums.pelicanparts.com/porsche-911-technical-forum/940876-mice.html#post9414265

review:

was it worth it?
Yes--everything as advertised--speed modulation best it has ever bee.

would I do it again?
Yes, if I knew then what I know now (all of the above stuff). If I were starting without the above info, I might consider hiring out the install--
reason to hire out:
1--I'm getting too old for this *****, rolling around under a 911 dash and engine compartment makes me sore & can't sleep at night
2--been there, done that, shiny's worn off; if I was younger and not as fat, I'd be more enthusiastic
3--I could afford to pay someone
4--reason not to hire out--I don't trust many people messing with my car.

level of difficulty?
If one is reasonably comfortable doing this kind of stuff, have at it. If you aren't, this might not be the first project you want to tackle. I had 4 yrs in Air Force electronics and a career in medical devices, much of it in electronics.

How hard can it be?
If you've got a friend who knows electronics, will hang close and work for beer, wot's the worse that could happen? Contact me if you have questions.

My schematic for integration
 

If any electrical wizards would like to suggest any changes or correct any circuit wonkieness, please chime in. I included pictures of the screen since screenshots were blank. As you can see the instructions are very LEGO like, plug and play. The only thing that requires minor fabrication/modification is the harness, it needs to be extended about 5 ft. Pure cut and solder of 18ga wires, with a little shrink tubing. I am trying to get all my ducks lined up before pulling the trigger on the install. extending the harness today. Since running the wires will entail a bunch of interior parts need to be removed or worked around, I want this to to be a one time pulling of the interior. The descriptions of wires are as Rostra used, where the Tempostat plug may or may not use the term, it is what I termed the equal.

http://forums.pelicanparts.com/uploa...1551807368.jpg


http://forums.pelicanparts.com/uploa...1551808404.jpg


http://forums.pelicanparts.com/uploa...1551807409.png


http://forums.pelicanparts.com/uploa...1551807439.png


http://forums.pelicanparts.com/uploa...1551808670.jpg


http://forums.pelicanparts.com/uploa...1551808670.jpg

Extended the Rostra harness by 5 feet. 8 wires 2 splices soldered and adhesive shrink tubing. It was like washing your hair 15-16 times.....

Beautiful write-up. Well done!

Robert

In the schematic you created I see tempostat control box pin 3 being used. Can you explain why pin3 is wired to the violet negative brake wire?
I believe pin 3 on tempo is output 12vdc power for the tempo motor? If that's the case then that pin is dead once you unplug the tempo control box?

I do like your idea of simply attempting to wire everything to the existing tempo control box harness. Nice and clean.

Sal,
Finally a wire wizard! As I read the schematic, pin 3 and pin 7 are a loop once the tempostat driven unit in the engine compartment is jumpered. Since the Porsche clutch switch is normally open, I am using the tempostat relay as a surrogate clutch switch, normally closed. Per the Rostra the clutch switch is wired in series to the violet wire.