Oshin11

Most of the wiring seems fine, I cant pin what it is, this points to faulty cruise control module but that makes little sense since I got it working the other day. I just saw the prices for these parts on pelican....ridiculous.

Oshin11

Ok I have eliminated everything except the clutch switch. I am not able to get a reading, my ohmmeter just says 1 whereas it should have a reading of infinity.

scarceller

Just wanted to report a few tthings I've learned about the Cruise Control in our Carrera's

I have an 84 Carrera and my cruise module is in the trunk to the left of the Master Cyl. Also the 84 - 85 wiring schematic shows the cruise connected to the 2 Brake Light switches on the master cyl. The only brake light switches in my 84 are the 2 on the Master Cyl.

BUT, others have reported (like 1988 owners) that hey also have a switch at the pedal cluster as well as the 2 switches on the master cyl. It seems Porsche made some changes after 1985 to the Cruise Control but I don't have the schematics for 86-89 cars so I'm not sure what was done.

scarceller

Here is the Cruise Controll test procedure from the Factory Manual

Amber Gramps

scarceller, great post. The switch on the cluster is the clutch trip switch. It also shows up on the '84 in the Bentley manual.

Oshin11

Yea I found my clutch trip switch but cant find the brake switch. All of the readings from my ohmmeter point to clutch switch being the culprit, but for some reason I doubt it. My doubts come from the fact that it works every now and again. While I am removing all the seats, consoles, etc just to get to the clutch switch I am thinking of recarpeting my car while I am at it.

Amber Gramps

You are removing seats and console to get to the switch? Hold on!

1 remove drivers side floor mat
2 remove wood floor board
3 the switch is right in front of your face


(come on Oshin, that line almost cost Pete his quote of the week spot)

scarceller

You don't need to remove any seats or console. Just the floor board behind the pedals.

Also, my 84 does NOT have any switch on the cluster for the brake pedal, I know for sure that 84 & 85 cars only have the 2 switches on the Master Cyl. Others with newer cars, a 1988 owner did say they have a switch on the pedal cluster for the Cruise. But my 84 does not, the cruise uses the switches from the master cyl in my car.

Your car is an 87 so I don't know for sure but it could be you do not have a switch pedal cluster so don't be surprised if you don't find one.

Does anyone have a wiring schematic for 86, 87, 88 or 89 cars?

Amber Gramps

scarceller, please read post #20.


when I posted that I had the scematics right in front of me. The switch is on the clutch!

now I'm at my office eating chocolate cake with the girls and about to run to south central so you are on your own.

dshepp806

scarseller: great pic/scan!!

Best,

scarceller

Douglas,

Sorry, thought you where talking about the brake switch not the clutch switch. I was rambling on about how my 84 does NOT have a brake switch on the cluster. But yes indeed it does have clutch switch on the cluster.

scarceller

I found the schematics for the Cruise Control for all years 84-89 and there was a change to the brake switch circuit. From the 85 and 86 schematic it seems that in 86 Porsche stopped using the switches on the Master Cyl for the Cruise and added yet another 3rd switch dedicated to the Cruise while using the 2 Master Cyl switches only for the Brake lights. Prior to 86 (84&85) they used the Master Cyl switches for the cruise.

Or are they simply only showing one of the Brake light switches from the Master Cyl? In any case the schematics are diffrent and they even have a diffrent name for the switch, thoughts?

Here are the schematics for 85 and 86:

Oshin11

Ive seen all these picture before I have a bentley manual, but trust me you have to have mini me hand to be able to remove the clutch switch without removing the console. Removing the console makes the job easier.

scarceller

Yes it is hard to work near that tunnel!

Here's another way to test the Clutch Switch, simply remove it from the equation. Here's how: it looks like the clutch switch simply grounds the TempoStat relay coil and this causes the relay to cut the power to TempStat Motor. So if you remove the relay and jumper pins 30 and 87a on the relay plug you have hard wired the TempoStat motor to the controller and the Clutch switch will be completely ignored.

Of course only do this for TESTING because in this configuration the cruise will still work even if you press the clutch in and the RPMs will go through the roof.

This way you don't need to go digging at the Clutch switch till you know it's bad.

Amber Gramps

scarceller, the best part about this is that Oshin is a grad student at UCSB. He should be in a lab learning how carbon fiber works or about how some other building block of life is constructed in nature. But no........He is messing with a cruise control module on an old hot rod. The tax payers, his parents, and his employer all think he is doing research but really he is playing with a 21 year old Porche. Only in America. The really funny part is that he's most likely the top of his class.