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Cruise Control Troubleshooting and Info

Discussion in 'Electrical & Audio' started by sonicbluezx3, Sep 22, 2012.

  1. sonicbluezx3

    sonicbluezx3 Full Access Member

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    Truck Year:
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    Long story short, I bought a simple lock up kit since my truck didn't have the system installed outside of the transmission. I replaced the wiring inside the transmission (Solenoid and pressure switch to the 4 terminal connector on the top... .it's a 700R4 btw). I ran the wiring up and through the firewall.

    They sent me a GM Cruise control switch which also has the terminals for the brake switch. It is my understanding that the terminals for the brake light are on the left in this picture, and the two on the right are for cruise control.

    I talked to the original owner and he said the previous owner before him had put on a cheap aftermarket cruise control. I want to make sure I have these connected right. I need two prongs to hook up the lock up, but I don't want to remove the wrong one. Is cruise control the only other thing that ever gets connected to that brake switch? And does anyone know if the brake light connector is the black one or the clear one, or what the wire colors are?

    Here's a picture of what I'm looking at:

    Installation instructions for my kit:
    http://www.700r4.com/tech/tcc/brake_install/index.shtml

    Picture of the switch with the connectors:
    IMG_1012_zpsada50db2.jpg
     
    Last edited by a moderator: Dec 6, 2012
  2. chengny

    chengny Full Access Member

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    The brake light part of the switch is furthest from the plunger - the one with the clear connector insulator. also, I'm color blind, but the schematic says brake light switch feed is light green and that wire looks kind of green/gray to me



    That should be a Custom Cruise III system. Here you go. Some basic info - probably more than you'll ever need, but it might help somebody else someday:

    Component locations (see the lower righthand corner for brake/CC switches):

    [​IMG]

    The Cruise Master system, used on all 1980---82 models and 1983 Caballero and El Camino, and the Custom Cruise III system, used on 1983---87 models except 1983 Caballero and El Camino, allow the operator to maintain a constant vehicle speed without continually applying foot pressure on the accelerator pedal. Both systems use vacuum to control a servo unit which alters throttle position to maintain the selected speed, release valves and switches which allow the system to be easily disengaged, and dash or steering column switches to control the system. The primary differences between the systems are the manner in which the servo is controlled and the method of sensing vehicle speed.

    [​IMG]

    1983---87 CUSTOM CRUISE III
    This system consists of a mode control assembly, electronic controller (module), Vehicle Speed Sensor (VSS) buffer amplifier, servo unit, and release switches and valves. The servo unit maintains vehicle speed (throttle position) by trapping vacuum in its diaphragm chamber at servo positions determined by the control module. The module monitors mode control switch position, signals from the VSS buffer amplifier, servo position and release switch operation, then operates vacuum valves within the servo unit to control servo operation and vehicle speed. The module also contains a speed limiting function which prevents system operation at speeds below approximately 25 m.p.h..
    The mode control assembly, Fig. 5, consists of a 3 position slide-type switch and a set/coast switch button. To operate the system, the slide switch must be in on position and vehicle speed must be above 25 m.p.h.. The system is engaged at the desired speed by fully depressing, then releasing the set/coast button. Cruise speed can be increased from set position by accelerating vehicle to desired speed, then pressing and releasing button. In order to decrease speed, the set/coast button is held in the fully depressed position (disengaging system), then released when the desired speed is reached. The system can be disengaged at any time by depressing the brake or clutch pedal, or by moving the slide switch to off position.
    If the system is disengaged by depressing the brake or clutch pedal, the last set speed will be retained in the module memory until the slide switch or ignition switch is moved to off position. Momentarily moving the slide switch to the resume/accel. position will cause the vehicle to accelerate to the last set speed and maintain that speed. If the slide switch is held in the resume/accel. position, the vehicle will continue to accelerate until the switch is released. When the switch is released, the speed that the vehicle accelerated to becomes the new set speed.
    The slide switch also allows a ``tap-up'' function to increase cruise set speed in 1 m.p.h. increments. With the cruise control engaged and operating, ``tapping-up'' is done by pressing the slide switch to the resume position, then quickly releasing it. This procedure can be repeated 10 times before the system must be reset to a new speed in the conventional manner.

    [​IMG]

    Servo Unit Operation
    The servo, Fig. 6, consists of a vacuum operated diaphragm, a normally open solenoid valve to vent the diaphragm, a normally closed solenoid valve connecting the diaphragm chamber to the vacuum source, and a variable inductance position sensor that provides the module with servo position data. The servo operates the throttle in response to control module commands as follows:
    When the system is engaged and operating at a steady rate of speed, both solenoid valves are closed. Vacuum is trapped in the diaphragm chamber exerting a constant force on the diaphragm and the throttle position remains fixed.
    When the vehicle is losing speed due to increased load, or when the operator seeks to increase speed through the control switch assembly, the module energizes the vacuum valve solenoid. This increases the force exerted on the diaphragm, which in turn increases the throttle opening.
    When vehicle speed increases above the pre-set cruise speed, or when the operator seeks to decrease speed through the control switch assembly, the module de-energizes the diaphragm vent valve solenoid. This opens the valve, decreases force on the diaphragm, and allows the throttle return spring to decrease the throttle opening.
    During normal operation, the module will pulse the operation of the vent or vacuum valves, as needed, to maintain the set cruise speed. The average duration of each pulse is 10 milliseconds. If vehicle speed drops 5 m.p.h. below set cruise speed, the module will hold the vacuum valve in the completely open (energized) position. If vehicle speed exceeds set cruise speed by 3 m.p.h. or more, then module will hold the vent valve in the open (de-energized) position. The module will hold the valves open until the vehicle speed matches the set cruise speed. The diaphragm vent valve will also remain in the fully open position if the brake or clutch pedal is depressed, the ignition is switched off, or if an open circuit exists in the system feed circuit or in the servo position sensor.

    Schematic and vacuum hose diagram:

    [​IMG]

    [​IMG]

    Diagnostic flow chart - for inoperative condition:

    [​IMG]


    Here's a link to a good installation procedure - with excellent visuals.
     
    Last edited: Sep 23, 2012
  3. oneluckypops

    oneluckypops Full Access Member

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    chengny may very well be right on which connectors are witch. I would have to test the switch to know for sure.
    But here's a little FYI for ya if i can explain how it works.

    The Brake switch is a 2 part switch, 1 side of the switch is (normally open) for the Brake lights. So when you press the brake pedal the switch CLOSES and sends current to the brake lights, but when the pedal is NOT depressed power is cut to the brake lights.

    Now other other side of the switch is what is referred to as a (normally CLOSED) switch. This side of the brake switch is used for, Converter lock up, as well as Cruise control. So when you press the brake pedal the switch creates an OPEN circuit which cuts power to the converter and/or the cruise control, then when you release the brake pedal the switch CLOSES and power is then again supplied to the converter clutch and/or the cruise module.

    You can test which part of the switch does what with a simple test light, or a volt meter.
    Connect test light to a KNOWN good ground, the back probe the connectors on each side of the switch. The brake light circuit should have 1 terminal hot at all times, when the other side of the connector will be Open, press the brake pedal and BOTH wires will then be hot.
    Then If you test the other side of the switch the key should have to be turned on, (ignition voltage). Pedal relaxed BOTH wires will be hot, push the pedal and only 1 of the wires will be hot. The wire that looses power with the pedal pressed would be the wire you are looking for for the TCC (torque converter clutch).

    I personally would rather use a digital volt meter set to check continuity, But I am use to working on computer controlled vehicles which requires you to use a DVM rather then a test light on a lot of troubleshooting.
     
  4. sonicbluezx3

    sonicbluezx3 Full Access Member

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    Wow you guys are awesome. I now know what the cut wire pigtail that was on my speedometer was for. Also makes sense as to why the black connector had t taps. Now ill b able to finish my lock up wiring.
     
  5. 89Suburban

    89Suburban Full Access Member

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    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  6. 1low4x4

    1low4x4 Full Access Member

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    This is an informative thread. I don't think this 84 truck had cruise but I installed the column out of my red 85 that did. So it has the switch on the blinker. Besides finding the servo, and the harness under the hood, and then running the vac lines, what else do I need to make cruise work?

    Thanks guys. I couldn't find any cruise control stuff for sale on LMC other than the switch on the column. Guess ill hit up the junkyard
     
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  7. gmachinz

    gmachinz Harnessworx Inc

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    I have a few NOS style complete TCC/cruise harness kits made up if anybody is interested. PM me for more info...these are 83-87 specific style.

    AB44B4D7-5868-492A-B709-E640B0234CC2.jpeg
     
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  8. Marcoman

    Marcoman Junior Member

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    Hey, I was wondering if the cruise control function would be compatible with an LS engine and say Dakota Digital gauge cluster? I'm leaning towards doing this someday on my '84 GMC which did NOT come with cruise control on the stock steering column. I was thinking of swapping it out for a tilt column that already has the cruiser control built-in factory. Am I looking at a possible can of worms? lol
     
  9. brewster21

    brewster21 Junior Member

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    https://www.dakotadigital.com/index...id=1004/category_id=477/mode=prod/prd1004.htm

    I believe my dad used this when he put cruise control on his ‘65 ls swapped impala. He just bought this kit and a Dakota digital turn signal lever with the cruise control controller built onto the end. Also make sure you read what specific ls motors this works on before you buy it, it’s listed in the description of the link I attached.


    Sent from my iPhone using Tapatalk
     
  10. 75gmck25

    75gmck25 Full Access Member

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    Back in the day there were a lot of aftermarket cruise controls sold, and they worked about the same as the stock system, so you should be able to add cruise control without any major problems. However, there are a few key points:
    - The vacuum servo uses a flexible, sheathed cable that must be routed so it lines up with the throttle linkage and can pull in parallel with the throttle cable. Various types of brackets are used to clamp it on next to the throttle cable and get it aligned. In many aftermarket units the final connecting link is a beaded chain so that it can pull the throttle, but will release quickly and not bind if shut down.
    - All units need input from a speed sensor. Many use a VSS inline with the speedometer cable, and for these you may have to use an OEM cable. Older aftermarket units used to use two magnets epoxied to the driveshaft and a sensor mounted so that it was about a 1/2" from the magnets. The sensor used the spinning magnets to sense speed.
    - You need a mechanism to shut it down when you press the brake or clutch. Good units will both shut it off electrically and also have a vacuum break that vents the vacuum servo and releases the cable. These are very key safety features.

    Bruce
     

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