ET RAM

I have been having a problem with my cruise control and could use a wiring diagram. I have not been able to find one. My Haynes manual does not show it.

The CC turns on but does not engage. I checked the usual fault, the vacuum line below the battery. It was eaten away. I fixed it. Still had a vacuum leak. Found a rubbber 90* boot by the pump with 2 holes. Fixed it, vacuum holds but still no CC.

So I moved on to the stop lamp switch. Tested the switch. Appeared good. Went to auto parts house and tested a new one. It tested the same as mine so I did not buy it.

The switch has 6 pins. Two are for the stop lights and it works when you step on the pedal. The other 4 pins make a connection with no pressure on the pedal. The 2 in the center are for the CC and it has power and complete circuit. The last 2 has power one but not the other. So there is a problem on that wire. Just not sure where it goes.

When I get a chance I will check at the servo. The center 2 wires appear to go to the servo. Not sure on the last 2. A diagram would be helpful.

Thanks.

bob4x4

ON-BOARD DIAGNOSTICS TEST
The Powertrain Control Module (PCM) monitors critical input and output circuits of the speed control system making sure they are operational. A Diagnostic Trouble Code (DTC) is assigned to each input and output circuit monitored by the On-Board Diagnostic (OBD) system. Some circuits are checked continuously and some are checked only under certain conditions.

If the OBD system senses that a monitored circuit is bad, it will put a DTC into electronic memory. The DTC will stay in electronic memory as long as the circuit continues to be bad. The PCM is programmed to clear the memory after 50 engine starts if the problem does not occur again.

DIAGNOSTIC TROUBLE CODES
Diagnostic Trouble Codes (DTC's) are two-digit numbers flashed on the Malfunction Indicator (Check Engine) Lamp that identify which circuit is bad. A DTC description can also be read using the DRB scan tool. Refer to Emission Control System for more DTC information.

A DTC does not identify which component in a circuit is bad. Thus, a DTC should be treated as a symptom, not as the cause for the problem. In some cases, because of the design of the diagnostic test procedure, a DTC can be the reason for another DTC to be set. Therefore, it is important that the test procedures be followed in sequence, to understand what caused a DTC to be set.

Refer to the following Speed Control Diagnostic Trouble Code chart for DTC's which apply to the speed control system. Refer to the appropriate Powertrain Diagnostic Procedures manual to diagnose an on-board diagnostic system trouble code.

RETRIEVING DIAGNOSTIC TROUBLE CODES
To start this function, cycle the ignition switch ON-OFF-ON-OFF-ON within 5 seconds. This will cause any DTC stored in the PCM memory to be displayed. The instrument panel mounted malfunction indicator (Check Engine) lamp will display a DTC by flashing on and off. There is a short pause between flashes and a longer pause between digits. All DTC's displayed are two-digit numbers, with an approximate four-second pause between codes.

An example of a DTC is as follows:

Lamp on for 2 seconds, then turns off.
Lamp flashes 1 time pauses and then flashes 5 times.
Lamp pauses for 4 seconds, flashes 3 times, pauses, then flashes 4 times.
The two DTC's are 15 and 34. Any number of DTC's can be displayed, as long as they are in memory. The lamp will flash until all stored DTC's are displayed. A DTC code number 55 signifies the end of tests.

If a DTC number 15 or 34 is observed, refer to the appropriate Powertrain Diagnostic Procedures manual. Correct any problems found in your diagnosis, then recheck for a DTC after corrections are completed. Use the DRB scan tool to erase a DTC after repair

SPEED CONTROL DIAGNOSTIC TROUBLE CODES
Diagnostic Trouble Code DRB Scan Tool Display Description of Diagnostic Trouble Code
15** No Vehicle Speed Sensor Signal No vehicle distance (speed) sensor signal detected during road load conditions.
34* Speed Control Solenoid Circuits An open or shorted condition detected in the Speed Control vacuum or vent solenoid circuits.
55* N/A Completion of fault code display on Check Engine Lamp.
* Check Engine Lamp will not illuminate at all times if this Diagnostic Trouble Code was recorded. Cycle ignition key as described in manual and observe code flashed by Check Engine Lamp.
** Check Engine Lamp will illuminate during engine operation if this Diagnostic Trouble Code was recorded.

bob4x4

SPEED CONTROL SERVO
For complete speed control system diagnosis, refer to the appropriate Powertrain Diagnostic Procedures manual. To test the speed control servo only, refer to the following:

The engine must be started and running for the following voltage tests.

Start engine.
Disconnect 4 - way electrical connector at servo Speed Control Servo Location
Turn speed control switch to ON position.
Check for battery voltage at pin - 3 of wiring harness 4 - way connector Servo 4 - Way Harness Connector This is the 12 volt feed from the stoplamp switch. When the brake pedal is depressed, voltage should not be present at pin - 3. If voltage is not present with brake pedal not depressed, check for continuity between servo and stop lamp switch. Also check stop lamp switch adjustment. Refer toBrakes for procedures.
Connect a small gauge jumper wire between the disconnected servo harness 4 - way connector pin - 3, and pin - 3 on the servo. Check for battery voltage at pins - 1, 2 and 4 of the servo. If battery voltage is not at these pins, replace the servo
Turn ignition switch to OFF position. Check for continuity between disconnected servo harness 4 - way connector pin - 4 and a good ground. There should be continuity. If not OK, repair open circuit to ground as required.

ET RAM

bob4x4,

Thanks for the info. I will work with it. Didn't think to check for a code. I will see if it is showing any. The servo info will be helpful.

I just could not figure out that last set of wires at the stop switch. One has power going in. The switch is good but I do not get anything going out. Just have to keep looking.

Thanks again.

ET RAM

Well,this morniing I was looking through my Haynes manual while having coffee. I found a diesel PCM schematic that is in the diesel fuel section and not in the emissions section where the other schematics are located. The schematic shows the wiring of the stop lamp switch.

I was totally wrong on the stop lamp switch wiring. The center 2 pins are for the RWAL. The 2 pins on the firewall side are for the stop lights and the 2 pins on the seat side are for the CC. This circuit is my problem. I get power on one side but nothing thru the switch. The wire goes to the servo. So I will be checking at the servo and also check for codes.

My battery was really corroded and I painted the area under the battery with a lead acid battery paint. The paint is holding up good. Hopefully it is as simple as a bad ground. I will keep looking.

dguru

Power goes through the brake lamp switch cruise control contacts when the pedal is up and switch is depressed. The most common problem is that the switch gets out of adjustment. If you remove the switch you will see it will "auto adjust" To remove the switch press brake pedal down and turn switch 30 degrees and it pops out. At that point push it back in with some force and twist it back to its original position. This resets the adjustment and it will auto adjust when the pedal is let up.

ET RAM

Thanks for the info. While going home today, I was thinking about the switch and what I posted this morning. It just didn't add up, so I am going to start at square one again. Now I have a better understanding of the circuit. The switch adjustment did come to mind. I never checked it installed in the truck. I checked it out of the truck. So, I will do as you say and take some more measurements and see what I have.

Thanks.

mechrisme

I am having the same problems too, my truck didn't have cruise control and I swapped all the parts and I got a servo and I tested it like its said before and it checks out, I tested a gas one I had too. I swapped the cables and bases thinking the base was messed up and it still didn't work. I know its somewhat of a different setup too. If the brake lamp switch wasn't aligned, would you still be able to test the servo? I had around .21 volts when testing the servo, is that right?

dguru

I have a basic stripped 94. It had the servo under the left battery from the factory but the truck was not spec with cruise. I checked the serial number.

I added cruise by changing the clockspring and adding the switches in the steering wheel. It worked after I got the brake switch adjusted right and some TPS work. The dealer said that it would cost me $800 to upgrade to cruise. I spent $30.

Later I added tilt, power windows, power locks, roof console, vanity visors, buckets, chrome bumper with driving lights, glove box lamp, cargo lamp and trailer harness. I also put a 1500 steering box on to give me a lower steering gear(1.75 turn to lock). There are lots of cheep upgrades with the C.A.R.S. program.

mechrisme

Would it still be possible to text the servo with the brake switch out of allignmeent since I was still gettting some voltage through it

dguru

You could jump power to pin 3. That will bypass the brake light switch. Might be easier to check for power on the wires at the switch. There are 6 wires on the switch.

The wire that runs between the brake light switch and cruise servo is DB/RD. The feed wire is YL/RD and should be hot when the ign. switch is on. If you don't have power on the DB/RD wire the switch is out of adjustment.

EDITED for wire color

mechrisme

I tested the wires by the servo like I read on here and it was difficult but I got it done. I got it done, I got voltage up there but not much.

dguru

Should be 12-14 volts on pin 3 DB/YE wire. If not look at the brake light switch.

mechrisme

it was like .21 or whatnot, I'm check for power at the switch

mechrisme

I check power at the switch and I didnt have any power and I think I readjusted it and still no voltage. Could the switch be bad even though the brake lights work?