Cruise control failure.

Thanks, Merlin.

The first thing I did was to replace the burnt out high mount brake light bulb, which wasn't just burnt out but apparently had overheated to the point the glass softened and bulged and had gotten hot enough to start melting the polymer socket! No difference.

I replaced a 22" length of 7/32" vacuum hose that ran from the PVC line to some other vacuum item down below the battery. I suspected it wasn't directly related by any means, but it was full of tiny cracks. No difference, though it was time to replace it anyway.

I poked around looking for the deactivation switch. It is not on the master cylinder or the brake line, but is at the end of a roughly 3/8" i.D. Vacuum hose that runs from the controller bolted to the LH shock tower, through the firewall, to a valve that pops open when the brake pedal is depressed. I dropped in to visit my friend Jeff at the local Ford dealership parts counter. With a bit of looking and head scratching, he called it a 'vacuum dump switch'. He looked for a diagram to print out, but all he could find was a schematic for the dealer installed speed control system, which appears to be nothing like the factory setup. He felt it was most likely the switch that had gone bad.

At home, I tried an idea to test it. I pulled the hose loose at the butt connector about six inches from the controller and plugged it, then plugged the end of the segment leading to the vacuum dump switch on the pedal. I took it out on the road nearby and at about 45 mph, I tried to set the system to see if it would take. No go, even after several attempts and some underhood fiddling to make sure everything was tight.

Upon my return, I hooked the hose back up and swiped the vacuum dump switch out of the '92 Taurus I keep handy for parts. The engineering numbers match, so it's the same part. No luck here, either.

There are two electrical switches acted upon by the brake pedal. I know one is for the brake lights, but what might the second one be? Could this be an electrical deactivation switch designed for redundancy? I did pop the cover of the fuse box, finally, but none were blown and all were in tight. I suppose I could check the one behind the LH shock tower, though.

This is beginning to be somewhat of a puzzle. The other thing I'm wondering: I never did replace the clockspring after the airbags deployed upon striking a large doe in April of '03. I've not gotten out the voltmeter or the test light yet, but I suppose it's possible an electical fault is there, though it's been fine for five and a half years until this last Sunday and the horn does work just fine.

Thanks again for any insight you may have!

Tim :)

Merlin,

I do appreciate your promt reply!

The car is equipped with standard factory speed control common to a second generation Taurus GL. Unfortunately, the only diagram my Ford parts man can conjure up from his computer is the dealer installed system, which looks very different from the factory system I've got!

I'll scratch my head on that second switch.

I checked for presence of a vacuum 'signal' at the control unit. At idle, the gauge indicated an utterly smooth 19" of mercury. Not bad for a 200,000 mile car - taking it easy and changing the oil really help!

At the farm, I 'spun up' the '94 Taurus wagon I bought my mother a few years back, only to have her 'cook' it a year ago when she decided not to stop when the thermostat stuck shut and caused it to overheat. It acts like a blown head gasket, so I fear the heads are warped. I'll find out for sure as soon as I tear it down for a rebuild one of these days! I filled the radiator, hooked up the battery, and drove it a mile and a half to verify the cruise on it worked - it did. I swapped my switches into the car yesterday, so I knew my problem didn't lie there! I switched them back. I swapped the 'vacuum dump switch', but to no avail. I swapped control modules. Nada.

I don't tilt the column much at all, but I still suspect an electrical fault somewhere, either in the wiring or in the clock spring, although again, the horn works just fine. Out come the test lights! If course, maybe the position of one of the switches on the brake pedal has somehow been knocked out of spec, but I can't imagine how.

I'll keep you posted as this develops!

Thanks again,

Tim :)

Okay, today's developments:

First, I hooked my vacuum gauge to the hose that terminates at the so-called 'vacuum dump switch' that opens when the brake pedal is depressed. Starting the car and taking it for a short drive reveal no vacuum signal present in the current non-functional mode of operation.

I pulled the harness connector from the control head and used the DMM to determine the presence and values of DC voltage at the six terminals inside. With the ignition off, no significant voltage anywhere. A few random hundredths of a volt, which to me generally means 'zero'. With the ignition lock advanced to the 'run' position, I read 10.75 VDC at one pin, and varying lesser values at a few other pins, and negligible values at the rest.

At the farm, I fired up the '94 for a quick test drive to see how it functioned with my '95's control head and 'vacuum dump switch' installed. I filled the radiator and put it into gear, only to discover I now suddenly have very little brake response! Apparently yesterday's drive 'blew' something in the system and most of the fluid was gone from the reservoir. Proceeding very carefully, I backed it out of our driveway and headed down the road for a quarter mile or so. At about 35mph, I toggled the 'on' and 'set/accel' switches. IT WORKS. Thus, my 95's switches, control head, and vacuum switch are just fine or this '94 wouldn't be working just fine!

Returning ASAP before anything could go wrong out on the road, I parked the car and let the coolant steam from the exhaust clear. I opened the hood and pulled the connector for a voltage check. Nothing at all with the ignition off. So far so good. I measured eleven and something volts at the same pin I got the strongest voltage from on my '95 when the ignition was energized, and NOTHING anywhere else. I imagine each of the remaining five pins would be somewhat congruent with the five switches (on, off, resume, set/accel, and coast) mounted to the steering wheel. Either something is shorting all of the wires so stray voltage signals are hitting the control head all at once, OR, much more likely in my opinion, there's a control module up under the dash that's gone haywire and has internally shorted or something to that effect. Now if I can only figure out where the heck the thing is, I may just be in business here.

Since my Ford parts man can't find a diagram of the factory system in his computer system at the local dealership, I might have some hunting to do here.

Thanks again!

Okay, for everyone who's been following this thread:

After eliminating practically everything short of the Vehicle Speed Sensor (VSS, and remember, the speedometer still works just fine!) And the wiring harness, I just put up with the situation for a while and kept randomly trying it to see if the problem would resolve itself. A most troublesome intermittent starter solenoid lead fault that used to be so irksome was like this. If I just held the key, after five or ten seconds it would usually start to crank when this happened. This occurred on and off for a month or two, perhaps every twenty starts or so. And then it just quit happening and hasn't happened even once in at least two years now. The truth: I just REALLY didn't want to start cutting and splicing wiring. My gut feeling was to not touch a thing.

One day recently, I replaced the fuel filter, which I hadn't done in a few years. It's just not a job I care for a whole lot, so I'd let it slide for awhile. Trying to run a diagnostic to see if any codes pertinant to the vehicle speed control (Ford terminology) could be found, I noticed while conducting the so-called 'goose test' that upon taking a brief stab at the accelerator, the engine didn't run so well above about 3000 rpm or so. At 201,000 miles, for all I know, maybe the valve spings are getting weak and the valves are starting to float. Or my fuel pump is developing less than the minimum 30 or so psi specified. Hmmm.I don't have a fuel pressure gauge, but I could pick up a new filter for $8, so why not? It was time, anyway.

Did it run smoother? Yes. And later that day, out on a back road near my home, I cycled the switches just out of habit. The system took hold and performed flawlessly. I've done this about a dozen times since then, and it now works like it always did.

I mentioned this to Jeff, my Ford parts man, who lives just down the street from me as he was getting in his F-150 to head back to the dealership at the end of his lunch hour. I haven't heard screaming hysterical laughter like that in a long, long time.

Never underestimate the power of coincidence. But, there may be a connection. My hypothesis: the engine was starting to starve slightly at highway speed, and the cutting out that resulted kept breaking the vacuum 'signal' the servo relied on in order to function. Or not. Who knows!

So - if your cruise control isn't working, my recommendation after checking for vacuum leaks, the Brake On-Off (BOO) circuit, et al, is to make sure your car is running right. Clean filters, good plugs and plug wires, fresh gasoline of known good quality, etc. Strangely, I didn't notice any hesitation or missing as I drove down the road, but punching it while in park sure was an eye opener. That might just be the test to perform - rev it up and see what happens. If it stumbles when you 'floor it', you may just have found the underlying cause for your cruise failure.

BONUS - I'm swapping out the fuel pump now before the 201,000 mile original fades away and leaves me stranded somewhere. Needless to say, I'll be installing ONLY an original OEM Ford pump, not some aftermarket item! The price for the Motorcraft unit from the dealer is really quite competitive, too. I consulted Jeff to learn what insight his years in the Ford/Motorcraft parts business may have imparted. He tells me:

1) The fuel tank must be removed to replace the pump, not just lowered from the vehicle. If you have ANY issues with the tank, such as rust, big dents, etc, now is a good time to replace it. You're already taking your current one out as it is.

2) Those filler tube rubber hoses that connect the steel tubes to the tank. BE CAREFUL. A new set is $150! Jeff recommends soaking them up with a silicone product like Armor-All, etc. You sure as heck don't want to be cutting them off with a knife like you would a stuck radiator or heater hose!

3) A Left Hand (driver's side) tank strap is $13. A Right hand one for the 95-down Taurus is discontinued and probably very hard to get. If you need either, you might take a look at what the aftermarket has available.

4) If you need to replace one of the two bolts holding the tank straps, they're 10mmx50mm. I'm not 100% sure of the pitch, but it looks like 1.5 would be likely as the threads were somewhat coarse. The bolts aren't too exotic, should you round or twist a head off (still use lots of penetrant - and, maybe it's just me, but torching anything near the fuel tank gives me the heebie-jeebies, so JB-80 and plenty of time are your friends here!) Jeff advises me the 'J-nuts' are obsolete, though. No reason a regular nut and washer wouldn't do the trick today, but if you ever have to go back in, getting a wrench on that nut may be a real bear. If you're long-term with your Taurus like me, try like thunder to save those nuts with LOTS of oil or plan on substituting a 'J' hook with a nut and as many washers as are needed to snug up that tank strap!

Oh, about fuel pumps. There are something like half a dozen different iterations to fit a Taurus. Generally the difference is in the sending unit, which will vary between tank sizes (16 gal. Std. Or optional 18.6 gal) and also between digital and analog fuel gauges, as well. There's also plastic or brass outlet tubes, but I'm not entirely sure what difference that'll make at this time. Jeff felt that if you're going with a relatively low-mile/low-time fuel pump scavenged from another Taurus, you'd be much better making sure the donor car has the same dashboard yours does and then just swapping the entire tank out. This way you don't have to replace the fuel pump gasket, don't have to mess with unlocking the retaining ring holding the pump to the tank, and best of all, you don't have to worry about getting the right pump/sending unit assembly for your particular gas tank.

Hopefully Jeff's advice will be of use to someone reading this!

Take care and good luck,

The TiGor

Hopefully I won't need to use any of the testing data you've generously posted, but it's sure nice to know its there because I'm sure there will be plenty of others browsing or searching the forum who'll be putting up with the same issue, and replacing a fuel filter might not do it for them. I'm still not absolutely certain it's what 'did it' for me. Never underestimate the power of coincidence!

Thanks again,

Tim 'the TiGor' Gordon