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Help with Diagnosis of Cruise Control Issue Requested

 
  #1  
Old 11-28-2010, 01:58 PM
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Help with Diagnosis of Cruise Control Issue Requested

Howdy folks,

This is my last thread (for now), I promise!

I have a 1986 F-150 Supercab with a 5.0L EFI power plant whose cruise control does not work and never has as long as I have owned this truck. Previously, I have replaced a faulty turn indicator switch successfully. I am in need of the assistance of a troubleshooter experienced with factory installed cruise control to walk me through the troubleshooting process or to link me to the process. I have looked through approximately 17 pages of threads from this forum, but I did not find any that I found helped me understand this issue.

When I had the steering wheel off to replace the turn indicator switch, I did not think to test the cruise control switches (nor do I know how to do this), but the switches seem to work normally. Under the hood, I have looked at the cruise control mechanism. It appears to be in good condition. The vacuum hoses are connected in what I presume to be the correct locations and do not show signs of cracking or excessive wear. There is a cable that goes to the fuel injection mechanism. It is in good condition. The electrical connector is intact. I have not crawled under the truck yet, and frankly I am hoping to avoid this, if possible. I have read that in this year of truck, the horn relay is a part of the cruise control circuit, however the horn on the truck works. I have also read about a separate relay/circuit component for the cruise control that is supposed to be located in the vicinity of the fuse panel, but I find nothing like this on my truck - I might be thinking of a different year truck, however.

I am sure that I have not completely troubleshot this issue since I haven't been able to find the cause of this issue, nor do I have the cruise control working.

Thanks in advance for helping me with this issue!

Frank
 
  #2  
Old 11-28-2010, 03:01 PM
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Pull the steering wheel off again and check the condition of the brushes that transfer the cruise switch signals from the moving wheel to the stationary column.
 
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Old 11-28-2010, 04:19 PM
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Originally Posted by Franklin2 View Post
Pull the steering wheel off again and check the condition of the brushes that transfer the cruise switch signals from the moving wheel to the stationary column.
Thanks for the reply, Dave. I will do as you recommend and report back. Can you please tell me what I am looking for in the brushes? Sorry, but I just don't know.

Frank
 
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Old 11-28-2010, 09:39 PM
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They had different systems through the years, but basically the switches are in the steering wheel, and they go around and around several times when you turn the wheel. To keep the wires from getting wrapped and twisted up, they have some sort of system that keeps electrical contact to the horn and the switches, and lets the steering wheel move also.
 
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Old 11-28-2010, 09:59 PM
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Thanks for clarifying that for me. So does that mean I should be able to take a VOM or a test light and measure some current flow in the stationary part of the steering column when the cruise control switch is pressed if the brushes are good? Does that make sense for you?

Frank
 
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Old 11-29-2010, 01:06 AM
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When you pull the wheel, the wheel will be dead. You could though, put your voltmeter on ohms, and then take a reading on the wheel. The ohms scale will use power from the battery in the meter, and give you a resistance reading. Each cruise button should give you a different ohm reading. That's how it sends so many commands on just a few wires, each button has a different resistance value and the cruise module detects this value and knows what button you pushed.
 
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Old 11-29-2010, 10:29 PM
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This evening, I found a Mitchell manual for my truck that I could buy and download. The section on cruise control is 8 pages long and gives a step by step breakdown on how to troubleshoot the cruise control including test values! It is awesome! I printed it out and plan on using it along with the excellent advice I've received here to see if I can sort out what's wrong with the cruise control and report back.

Frank
 
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Old 11-30-2010, 04:22 PM
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Well, I spent the better part of the afternoon out in the cold and snow checking the fuses for the cruise control and checking the resistance of the cruise control switches as prescribed. For the benefit of future members who may find themselves troubleshooting cruise control switches, here is the procedure:

1) Disconnect 6-way connector at (speed control) amplifier (bottom edge of the dash to the right of the steering column). Check battery voltage at Lt. Blue/Black wire when "ON" switch is depressed. Battery voltage should be available from Lt. Blue/Black wire leading from control switches.

2) Connect an ohmmeter between Lt. Blue/Black wire and ground. Check wire for continuity to ground with "OFF" switch depressed. If resistance higher than 1 ohm is found, wiring, slip rings or switch is at fault, or steering column may not be properly
grounded.

3) To check steering column ground, connect an ohmmeter between a good body ground and steering column upper flange. Resistance should be less than 1/2 ohm. Rotate steering wheel, and check flexible coupling for resistance less than 1 ohm. If resistance higher than 3 ohms is noted, clean horn brush contacts and ground brush.

4) A resistance less than 1 ohm must be obtained before performing remaining tests. With ohmmeter connected between Lt. Blue/Black wire and ground, depress and hold "SET-ACCEL" switch. A reading of approximately 680 ohms should be indicated on ohmmeter.

5) Depress and hold "COAST" switch. A reading of approximately 120 ohms should be indicated on ohmmeter. Depress and hold "RESUME" switch. A reading of approximately 2200 ohms should be indicated.

Also, the shop manual I am using (Mitchell's) states that there are three fuses that are involved with the speed control (cruise control). They are nos. 1, 4 and 12. All three of these fuses were checked and found to be good. Can anyone explain to me why the cruise control requires three different fuses? That just doesn't make any sense to me.

Now that these steps have been completed, what's the next step in the troubleshooting process?

Frank
 
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Old 11-30-2010, 04:38 PM
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Did you check your servo/vacumn thing under the hood? I just bought a ford 250 and the owner said that the servo was garbage and they can't be had. I don't know how true this is I haven't looked but may be something to look at.
 
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Old 12-01-2010, 12:42 AM
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Now that these steps have been completed, what's the next step in the troubleshooting process?
Look in your diagrams, there should be a signal coming from a switch on the brake pedal. If it thinks the brake pedal is depressed, then the cruise will not work. Also on the brake pedal I believe there should be a vacuum line going to a switch on the pedal. This dumps vacuum from the servo so the speed drops off quickly when you touch the brake pedal. If this line is off, or the switch is leaking vacuum, then the servo will never work since it can't build vacuum.
 
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Old 12-01-2010, 09:36 AM
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Sounds good Dave. My back's kinda sore from my under dash escapades yesterday, so I'm not sure if I'm going to try tackling this today. I'll let you know what I find.

Frank
 
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Old 12-01-2010, 01:55 PM
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Fuse Number 1: 5 amps Instrument panel lighting. Have no idea why this would be used with the cruise control

Fuse Number 4: 20 amps Cigar lighter and Horn. The cruise control uses power from the horn circut to power the cruise control switches. This is why a horn relay is required with cruise control models.

Fuse Number 12: Spare this fuse is not used in factory applications and is for aftermarket accessories.

Source: 1986 Ford wiring diagram. The Mitchell diagram is different with the fuse panel numbering at least as it differes from Fords. Does not mean they are wrong though as the positions in the panel may be correct. They may not be as well. Double check.

I did some double checking and found these are required for the speed control to work.

Fuse Number 4: As stated above.
Fuse Number 11: Horn with speed control (Speed control amplifier) Main power for amplifier.
Fuse Number 13: Stop lamp switch and emergency flasher. When the stop lamps are switched on, like pressing the pedal to slow down, this also sends a signal to the speed control amplifier. Shuts down the cruise when the brakes or the clutch is pressed.

Again this is sourced from the 1986 Ford wiring diagrams.


You never said what transmission type you have. Manual or Automatic. There is a clutch switch on the manual transmission that disengages the cruise when the pedal is pressed. etc...
 
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Old 12-02-2010, 03:55 PM
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My truck has an automatic transmission, so the clutch switch is moot.

Looking at the switch on the brake pedal, it has a white shaft that contacts the arm of the brake pedal up under the dashboard and is in front of the brake pedal arm. It appears to be connected to vacuum tubing. To me, it appears as though as the brake pedal is depressed, the plunger on the switch is extended which causes the vacuum from the servo mechanism to be dumped. Is this correct? If so, then it may be that the switch needs to be adjusted closer to the brake pedal arm since the switch plunger does not appear to move when the brake pedal is depressed. Any advice on how best to go about making this adjustment? Neither Mitchell's nor my other manuals offer any suggestions.

Thanks!

Frank
 
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Old 12-02-2010, 09:12 PM
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You can pinch this line shut or plug it, and see if that's your problem. With the line pinched, if it starts working, when you hit the brake pedal to disconnect the cruise, it will slowly lose speed instead of dropping out right away. I can't remember how it adjusts, but it's probably some cheesy snap clip or something that likes to break. Ford loves to fasten things together with cheap plastic parts that break(though Ford is not the only one at fault for this).
 
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Old 12-03-2010, 10:51 AM
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Like glovemeister said, the servo needs to be checked. I had a cable break off in the servo where it connects to the 'clevis'. Also, vacuum lines need to be inspected for cracks. I also had the cruise cable fray where it comes out of the sleeve by the throttle - I replaced the cable with a bicycle brake cable I got at a bike shop.

I also have had issues with the vacuum dump switch you see under the dash on the brake pedal. By all means make the adjustment so that plunger moves. That's probably the easiest and cheapest fix at your disposal. THose plastic parts don't last forever. Good luck.
 

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