Cruise control not working

[colinrich76]

I have an 88 B2 and I cannot get the cruise working. I ran by a local junkyard and was able to pull a donor servo and a few speed amplifier modules. None of these did anything to get it working. I've checked for vacuum leaks and also checked the switch at the top of the brake pedal, all of these are good. Fuse is also good. I also pulled off the steering wheel cover and checked all of the contacts for the buttons, all looked good and had good contact. Throttle for the cruise servo is also adjusted appropriately.

All of this to say, I'm totally stumped. I've got to be overlooking something here. I've scoured the forums and haven't found anything that I haven't tried (listed above).

Anybody got any ideas?

 

[JerryC]

Any mods done to the truck? I think I read a post somewhere that LED tail/brake lights mess with the CC.

 

[Jim Oaks]

The electronic cruise control system consists of the following components:

Control switches
Servo/control unit (throttle actuator)
Speed sensor
Stoplamp and deactivator switches

The throttle actuator/control unit is mounted in the engine compartment and is connected to the throttle linkage with an actuator cable. The control unit regulates the throttle actuator to keep the requested speed. When the brake pedal is depressed, an electrical signal from the stoplamp and deactivator switches return the system to stand-by mode. This system operates independently of engine vacuum, therefore no vacuum lines are required.

Fig. 2: Electronic cruise control system components

 

[Jim Oaks]

The vacuum controlled cruise control system consists of the following components:

Control switches
Servo (throttle actuator)
Speed sensor
Clutch switch (manual transmissions)
Stoplamp switch
Vacuum dump valve
Amplifier assembly

The throttle actuator is mounted in the engine compartment and is connected to the throttle linkage with an actuator cable. The speed control amplifier regulates the throttle actuator to keep the requested speed. When the brake pedal is depressed, an electrical signal from the stoplamp switch returns the system to stand-by mode. The vacuum dump valve also mechanically releases the vacuum in the throttle actuator, thus releasing the throttle independently of the amplifier control. This feature is used as a safety backup.

 

[Jim Oaks]

Hope something there helps.

Vacuum circuits can be a pain, so you really have to check those closely.

Let us know what you figure out.

 

[colinrich76]

Thanks guys!

No mods done, it's all stock electrically.

Thank you for the diagrams! The stoplight switch looks brand new(just bought the b2 a month ago), but it's worth replacing just to check. The vacuum lines are solid, which is where I figured initially the issue would lie. Throttle actuator is solid, it just doesn't seem to turn on. I'll keep tinkering and keep you guys posted!

 

[colinrich76]

Alright guys, quick update:

I crawled under the B2 to check the speed sensor and there is no wiring harness plugged in! So, that would do it, I just can't seem to find what should plug into it, there are no open plugs in sight. So I'm assuming the speedometer cable was changed, but changed to one that doesn't have the cruise option? I'm not totally sure what else could have happened here.

 

[colinrich76]

Well, that may have been a problem, but not THE problem. Went ahead and replaced the VSS and the connector for the cruise. Nothin. Man, I was almost certain that would get it.

 

[Jim Oaks]

Here's a wiring diagram:

And here is a .pdf version of it:

http://www.broncoiicorral.com/library/diagrams/88_b2_body-2.pdf

 

[JerryC]

do the hazards work?

 

[colinrich76]

Thanks for the diagram!

Yes, the hazards are working.

 

[colinrich76]

Not sure if this matters, but the wires to my vss are different colors than the diagram specifies. Both are light blue, one with a strip of black.