Almost solved - Anyone has CC schematic for 1999 Limited?

[1998Exp]

Troubleshooting the CC in my 1998 Limited. I have the 1998 EVTM, but the schematic does not match reality. Because it's a late 1998, there is a chance that a 1999 schematic will be closer. If you have one, please post, thanks!

Details: CC worked intermittently, then died.
Diagnostics don't work, but I believe that they don't apply to the Limited with its additional functions on the steering wheel - they never worked, even when the CC was fine.
I checked the clock spring and it's fine. The switches on the left side of the steering wheel that control the CC all work and produce the right resistance, except for "resume," which appears to have a burned resistor. There is obviously more to it, because the CC won't even engage. The servo itself appears to be fine (I substituted another one, and no change). The clock spring shows continuity on all circuits and to the servo. Not so sure about connections inside the steering wheel between the clock spring and the push button assembly, but that's where the schematic does not match reality.

 

[J_C]

This is all I have, attached PDF. I've never worked on my CC but based on the wiring diagram, appears to use a resistive voltage divider to change sensed voltage on the controller "Speed Cont SW In" light-blue/black wire. You could calculate out what that voltage should be based on 1000ohm divided by any of the resistor values show.

For example with ~12.6V input, 1000 ohms in series through the switches and a divider pull down value of 680 ohms for Set/Accel, should result in about 5.1V at the Speed Cont SW In", with CC on and while holding in the Set/Accel button of course, and should have the whole ~12.6V at Speed Cont SW In, with CC on but no buttons pressed.

https://ohmslawcalculator.com/voltage-divider-calculator

Don't overlook that the circuit also depends on the controller having a good ground, so essentially just taking a multimeter and checking for correct values everywhere and low resistance between both ends of each of the two wires between steering wheel and controller. Not sure how much more to mention, like that if your horn works that should be evidence that you're getting 12V to the steering wheel but you could measure for 12V at the CC switches too, before and after the on/off switch, or check fuse 10 first.

 

[DR98FL]

In the 98 Ford manual look on page 55-4 EATC control. IT is the correct diagram for the limited's extra steering wheel controls.

It is the same for the Feb 99 ford manual. I got both.

 

[1998Exp]

Thanks a lot, J_C !
Unfortunately, the schematic that you provided, albeit drawn a lot clearer than the one in the EVTM is no different and has the same discrepancies. For example, the G108 ground does not go through the clock spring, and the only ground reference is the one arriving from pin 7 of the servo. Seems that this change was implemented when they switched the illumination to LEDs, which need much less current, of course. Speaking of those, the little board with the switches is a lot more complicated than what the schematic shows, and includes a couple transistors, a bunch of capacitors, etc., all appearing to be related to regulating the LED output in response to the setting of the dimmer for the interior light.
I am going to replace the burned resistors on this little board and see what happens. It's going to take a few days, because I don't have a kit of 1206-sized resistors and had to order those (no room there for wired ones). For the chosen few that may be experiencing something similar with those steering wheel mounted controls in their high trim 2nd Gen Exes, I will post my progress - if any

Incidentally, the ON/OFF contacts are momentary, so that 1K resistor shown on the schematic -- which seems to be a 0 Ohm trace on the actual board -- does not enter the equation for calculating the voltage presented to the servo when any other button is pressed. That resistor (or a current source) must be internal to the servo.

 

[1998Exp]

In the 98 Ford manual look on page 55-4 EATC control. IT is the correct diagram for the limited's extra steering wheel controls.

It is the same for the Feb 99 ford manual. I got both.

Thanks, I suspected so but had to ask anyway. Seems that they made some changes to the design but kept the earlier, perhaps Gen 1 schematic page in the book.

 

[J_C]

Thanks a lot, J_C !
Unfortunately, the schematic that you provided, albeit drawn a lot clearer than the one in the EVTM is no different and has the same discrepancies. For example, the G108 ground does not go through the clock spring, and the only ground reference is the one arriving from pin 7 of the servo. Seems that this change was implemented when they switched the illumination to LEDs, which need much less current, of course. Speaking of those, the little board with the switches is a lot more complicated than what the schematic shows, and includes a couple transistors, a bunch of capacitors, etc., all appearing to be related to regulating the LED output in response to the setting of the dimmer for the interior light.
I am going to replace the burned resistors on this little board and see what happens. It's going to take a few days, because I don't have a kit of 1206-sized resistors and had to order those (no room there for wired ones). For the chosen few that may be experiencing something similar with those steering wheel mounted controls in their high trim 2nd Gen Exes, I will post my progress - if any

Incidentally, the ON/OFF contacts are momentary, so that 1K resistor shown on the schematic -- which seems to be a 0 Ohm trace on the actual board -- does not enter the equation for calculating the voltage presented to the servo when any other button is pressed. That resistor (or a current source) must be internal to the servo.

I don't know if it matters, because G108 is only for the horn, but it pretty much HAS to go through the clockspring, no? I mean that's how the horn relay coil grounds, horn is triggered when you press the steering wheel to activate it. See attachment. If they changed that, then how does your horn relay get energized?

The only ground the CC circuit should need is through the servo controller.

You can use a multimeter on the metal end caps of the resistors to see if they are approx the right values or truly burnt to an open circuit state, then if they are just cracked off the PCB solder pads, reflow solder them back down.

Check on whether your model year uses a different CC servo controller. If it does not, then it is unlikely that the 1K resistor is in it but rather in the clockspring assembly as prior years where. You can also check this by measuring resistance between pins 1-2 while the CC switch is turned on. If they got rid of the separate ground for the horn relay G108 and instead the ground through the servo controller is now dual purpose, then it definitely can't have the 1K resistor in series there, because the horn relay wouldn't work with 1K resistance between it and ground.

 

[1998Exp]

I don't know if it matters, because G108 is only for the horn, but it pretty much HAS to go through the clockspring, no? I mean that's how the horn relay coil grounds, horn is triggered when you press the steering wheel to activate it. See attachment. If they changed that, then how does your horn relay get energized?

The only ground the CC circuit should need is through the servo controller.

You can use a multimeter on the metal end caps of the resistors to see if they are approx the right values or truly burnt to an open circuit state, then if they are just cracked off the PCB solder pads, reflow solder them back down.

Check on whether your model year uses a different CC servo controller. If it does not, then it is unlikely that the 1K resistor is in it but rather in the clockspring assembly as prior years where. You can also check this by measuring resistance between pins 1-2 while the CC switch is turned on. If they got rid of the separate ground for the horn relay G108 and instead the ground through the servo controller is now dual purpose, then it definitely can't have the 1K resistor in series there, because the horn relay wouldn't work with 1K resistance between it and ground.

Note that this schematic is grossly simplified and it lumps the switch assembly with the clock spring. They are actually two totally separate parts, in different locations. The clock spring has, in fact more springs -- two that serve the airbag and two that serve the second set of switches which operate the EATC and the radio.

Not 100% sure, but looks like they are indeed grounding the low side of the horn relay through the servo ground connection and that 1K resistor is just a piece of trace. What seems to be the G108 ground is actually connected to a pin on the clock spring harness connector, but it doesn't go to the clock spring, and instead just appears to go to the servo -- perhaps that's the way to assure that there is a ground connection to the push button assembly, even if the servo is removed. This ground is needed not just for the horn and CC, but also for the second set of switches, to work the EATC and the radio (which work just fine) - I found a black wire going to there. Kind of convoluted, but but should work.

And yes, pushing the ON switch creates a short between pin 1 and 2. It's one of the first things I checked when trying to figure out this little circuit board after noticing that it doesn't match the schematic (unlike the cheap Ford electronic of that era it's actually FR4, double-sided, with a green solder mask that makes following traces a challenge.)

That 2.2K resistor is an open, for sure. It's also discolored, obviously from overheating. So how does a 1206 size (usually rated 125mW), 2.2K resistor burn with no more than 14V applied? Probably a manufacturing defect that caused the resistance to go down over time. There is also a second 2.2K, same physical size on that board (function unknown) that looks overheated an measures about 600 Ohm - ha!

So is following all this nonsense worth my time? Not sure, but considering that the dealers want $400 for a clock spring and those switch assemblies are only available used in unknown condition, substitution doesn't look like a good troubleshooting strategy.....

 

[J_C]

It is not in front of me, so I can't be 100% certain, but it seems there must be at least a couple things you are assuming rather than proving through measurements.

While it is not electrically impossible to ground a horn relay through cruise control, it is very unlikely.

While it is not electrically impossible for a resistor to fail to a lower resistance state, it is extremely unusual, only case I can think of is a wire wound resistor with a ceramic carrier where a water, flux residue mixed and saturated it. There is no other defect I know of where a resistor can function at proper value then later through defect, drop in resistance. Discoloration is not necessarily evidence of a failure. I just mean that I don't know when what I'm reading is assumption versus your having measured values with a multimeter.

Are you measuring resistance in-circuit? That cannot be done unless you draw out a comprehensive schematic to be sure there aren't parallel paths reducing the values measured.

Ford using a PCB trace as a 1K resistor? It's extremely unlikely. There is little if any past history of them doing this and why would they do that dodgy design for one resistor out of the 4 of them but not the other 3? In theory you can make a trace a resistor but it just isn't something a major automaker does because it is not as reliable, unless just talking about someone calling a burnt up pcb trace a "0 ohm" resistor when that's not at all what it was, rather it just wasn't designed to handle much current so it melted from a fault.

If you have a PCB trace that is long and squiggly like they meant for it to have a long enough path to be 1K ohms, I'd love to see a pic of that.

I'll just throw this out there: I suspect the circuit is exactly as shown in the wiring diagram I linked previously except for the addition of an LED driver circuit in series for the LEDs where the incandescent bulbs were previously.

I could be wrong, but if you only have the one 2.2K resistor burnt, replacing that shouldn't make a difference except for that one switch function.

I have no motivation to disagree with you except to fix your vehicle.

 

[1998Exp]

It is not in front of me, so I can't be 100% certain, but it seems there must be at least a couple things you are assuming rather than proving through measurements.

While it is not electrically impossible to ground a horn relay through cruise control, it is very unlikely.

Actually, it doesn't seem to be grounded through the cruise control, only through its harness. Weird, I know.

While it is not electrically impossible for a resistor to fail to a lower resistance state, it is extremely unusual, only case I can think of is a wire wound resistor with a ceramic carrier where a water, flux residue mixed and saturated it. There is no other defect I know of where a resistor can function at proper value then later through defect, drop in resistance. Discoloration is not necessarily evidence of a failure. I just mean that I don't know when what I'm reading is assumption versus your having measured values with a multimeter.

Are you measuring resistance in-circuit? That cannot be done unless you draw out a comprehensive schematic to be sure there aren't parallel paths reducing the values measured.

Well, that 2.2K in the "RESUME" circuit measures as an open in the circuit - anything in parallel would only reduce it to some finite value. Just like you, I can't recall ever seeing a resistor that out of the blue reduced its value. It might have just failed open due to mechanical stress - go figure... As for the other (function unknown) 2.2K resistor measuring around 600 Ohm -- it can definitely be due to something in parallel. When I take it off for replacement I'll know for sure. Don't expect this one to make any difference -- it seems to belong to the LED driver circuit.

Ford using a PCB trace as a 1K resistor? It's extremely unlikely. There is little if any past history of them doing this and why would they do that dodgy design for one resistor out of the 4 of them but not the other 3? In theory you can make a trace a resistor but it just isn't something a major automaker does because it is not as reliable, unless just talking about someone calling a burnt up pcb trace a "0 ohm" resistor when that's not at all what it was, rather it just wasn't designed to handle much current so it melted from a fault.

If you have a PCB trace that is long and squiggly like they meant for it to have a long enough path to be 1K ohms, I'd love to see a pic of that.

Oh, I didn't claim that they created a 1K resistor by a long, squiggly trace (that used to be the practice in thick film hybrids with resistive inks, but definitely not here). All I wrote is that where that resistor is in the schematic I see a short piece of trace instead = 0 Ohms.

I'll just throw this out there: I suspect the circuit is exactly as shown in the wiring diagram I linked previously except for the addition of an LED driver circuit in series for the LEDs where the incandescent bulbs were previously.

I could be wrong, but if you only have the one 2.2K resistor burnt, replacing that shouldn't make a difference except for that one switch function.

Agreed, that's why I am not expecting to solve the problem of the completely inoperative CC just by replacing that one resistor. We'll see what happens next...
I will let you know what I found after Digikey kindly sends my 2.2K 1206 resistors (27 cents for a strip of 10 + $5 or so shipping) -- we'll have more fun discussing this!!!

 

[J_C]

I have to attend to other things so good luck, can't monitor this topic any longer.

You should critically review what I've already written, and MEASURE with a multimeter. This all comes down to whether the voltage values are what they should be at any given point in the circuit. Measure.

 

[1998Exp]

Almost there: the main problem was the servo. It failed, and the replacement that I installed was also bad - something that I did not suspect and which sent me on a wild goose chase. I finally "borrowed" the servo from my 2004 Crown Vic, and things came back to life. These servos - at least the earlier ones - obviously had a design flaw: this was the third one that failed in my Ex. The problem is obviously electronic, because the motor and the gears were in perfect condition. Unfortunately, there is no schematic available for the circuit board attached to the servo.

Also, the 2200 Ohm resistor connected to the RESUME button in the steering wheel assembly was burned or cracked open. An easy fix

And, to continue to prior discussion with J_C: I confirmed that the schematic in the EVTM is wrong and there is only one ground in the steering wheel, serving all the remote functions AND the horn. This is as weird as it gets: the ground is picked up at the steering column and goes to the servo, which sends it back on another pin, through the clock spring. Unplug the servo and the horn doesn't work! It's the same thing in my 2004 Vic. Why? I can't think of anything other than saving a few pennies by deleting one of the springs. To the Vic's EVTM credit, it has the correct schematic. Seems that they made the change at some point (perhaps going from Gen 1 to Gen 2) and kept the old schematic in the Ex EVTM. Incidentally, as discussed earlier, that 1000 Ohm resistor in the schematic that feeds the ON button was indeed removed and replaced by a short. One more penny saved. That detail is also correct in the Vic EVTM.

To the select few that may be chasing a similar problem: the CC self-test does not work for the high trim models, with the climate and radio controls on the steering wheel. If the CC fails, the servo is the prime suspect, and substituting "a known good one" is the diagnostic technique.

 

[1998Exp]

One additional piece of advice which resulted from chasing this problem: to the best of my ability to determine, all the Ford CC servos manufactured from the mid-1990s to the mid 2000's are identical, despite the plethora of part numbers and vehicle models listed for those part numbers by the sellers. The only difference is the mounting bracket - which is easily transferred. Also, if you are purchasing one, make sure it can be returned - preferably at the seller's expense. Some sellers claim "refurbished," "tested good," etc., but appearances are misleading, the failures are mostly electronic, and I seriously doubt that any of these sellers has the ability to test.