The cruise control troubleshooting chart has a GLARING ERROR. The test that states
"Measure ohms from pin 3 to ground, depress clutch pedal, and the meter should read 10 ohms." is dead wrong! If you look at the wiring diagram below with the control unit unplugged, you will see there is NO WAY to get a 10ohm reading between ground and pin #3. I troubleshot my CC using the chart and could not get the 10ohms, so I traced the circuit.
The clutch switch contacts are "normally open" when the clutch is at rest. When you press the clutch, the switch contacts close and provide ground to the "Tempostat" relay on pin #85. This "picks" the relay and opens the relay contact path from pin #3 to the tempostat motor, deactivating CC.
The clutch switch is hooked to ground and ONLY goes to the relay coil. There is NO PATH to pin #3. Ergo you can't ever get 10ohms from ground to pin #3.
The absolute way to check if your clutch switch is operating is
1. pull the Tempostat (cruise control) relay
2. connect ohmmeter one lead to ground, the other to pin #85 of the tempostat relay plug. Should have no continuity, then depress the clutch and you should read 0 ohms (continuity) That is an ABSOLUTE TEST of the switch!
I don't know how many folks have been led down the "garden path" by using the trouble shooting chart in the Bentley, and thinking they have a bad or maladjusted clutch switch. But I'll bet it's quite a few!
I'm not the first guy to discover this error, see the quote below from a couple of years ago!
Quote:
Originally Posted by dlshady
Guys,
I know this has been discussed to death here but I've read through EVERY single thread that contains anything related to the cruise system and haven't found anything close to what I'm experiencing. Hopefully there's somebody out there that has been down this road before that can shed a little light on the problem for me.
Here's what I got: 83SC with a completely inoperative cruise system. I've been through this system from front to rear several times now, and this is what I come up with:
The schematic and the troubleshooting chart (Table C) in the Bentley manual don't jive. The second step in the chart shows that depressing the clutch pedal should result in a reading of 10 ohms between pin 3 and ground, but the schematic shows that depressing the clutch should merely ground the tempostat relay and interrupt the circuit on pin 3 between the cruise amp and the servo. In checking pin 3, I do NOT have 10 ohms to ground when pressing the clutch pedal, but I DO have an interruption in the circuit back to the servo. When checking resistance between pins 3 and 7 I have @15 ohms (this is the resistance of the servo and the wiring back to it), and it goes to open when the clutch is depressed. So by my logic, checking the circuit this way verifies that 1) the servo has the correct resistance, 2) the wiring back to it is indeed good, 3) the clutch switch and tempostat relay are working as they should.
So: - The clutch switch is good
- The brake light switch applies @11.8 volts to pin 6 when the brakes are applied
I'm at the end of my rope with this car and I'm literally about ready to push it outside with the keys in it, hoping that some poor sucker will steal it. |