I have a problem with the cruise control not working. I just purchased this vehicle and can not find any info about the cruise control. What type of cruise control is this electronic or is it vacum and does anyone know where to get a schematic or diagram for it ? I have already checked the Haynes manual and can not find it there.
Greetings,
First thing, a few basics about the cruise control for this truck. You must be doing at least 25-35mph (depending on whether you have an automatic tranny or manual) before it should engage. It will disengage anytime you push the switch on the turn signal lever to the Off position, you press the brakes enough to make the brake lights turn on, you press and hold the decel button long enough for the truck to drop below 25/35mph, or you push in the clutch. The switch (as mentioned) is located on the turn signal and has three positions: Off, On, and Resume/Accelerate. There is a button on the very end of the turn signal lever for Set/Decelerate.
The main "box" for the CC is bolted to the firewall on the driver's side under the hood. The cable runs from the control box to the throttle plate for the throttle body and connects to it directly next to the throttle cable that comes in from the gas pedal. There is a fuse either in the fuse center under the dash or the electrical center under the hood for main power for the CC, and a relay under the dash that is triggered by the controls that switches the power when you set your speed.
If none of this sounds familiar, then you might have an aftermarket unit installed (some of which used replacement turn signal levers that looked and acted exactly like a factory unit). If you do then read no further - I'm only familiar with the factory units.
There are a few items that could cause the CC not to work. First thing is to go under the hood and check the connection and freedom of movement for the CC cable at the throttle body. Move the lever for the throttle plate by hand and see if the CC cable is free or jammed. There are two types of connections for the cable end to the throttle plate lever - fixed and free. If it's fixed (cable end hard bolted to the lever) and you move the lever the cable should move with it and that's OK. If the cable binds up and bends unnaturally, that's not OK. If you have a free end (cable end pulls against the lever but if the lever is moved manually then the cable does not follow it), if the cable moves freely when the lever is moved then that is bad (broken cable). Clear as mud.
Next, check the main power fuse and the relay under the dash. Also make sure that your brake lights aren't alway on (which would disable the CC). In later models (not sure about the '91), if the engine was having a problem then the ECM would disable the CC (my '95 with the diesel was like that). Those are the easy things.
The harder things are a bad control switch on the turn signal lever, bad wiring (especially inside the steering column), loose connection, or bad ground. Mechanically, if someone has removed and replaced the CC cable, there is a flat ribbon connection that runs from the servo inside the CC module and connects to the cable to pull and push it as it needs to increase or decrease throttle. The problem is that the cable can be attached to the module in two directions (rotated 90 degrees but still look OK when mounted). If the ribbon inside the module has been bent or twisted, it may not want to extend or retract and push/pull the cable.
If you have an aftermarket unit that uses engine vacuum to move the cable, then my only suggestion is to check for leaky or blocked vac lines.
Good luck - Jonathan
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