Bad brake pressure switch?

[1998Exp]

Noticed intermittent disengagement of cruise control in my '98 Limited. For whatever reason, self-diagnostics of the cc servo don't work in this model - perhaps because there are more buttons on the steering than in the plain vanilla models. When the cc failed, some years ago, I was forced to take a guess and replace the servo -- which fixed it. But then it refused to engage, while now it abruptly disengages in a random fashion. My suspicion falls on the notorious pressure switch that caused fires in the past. Ford's cure was to add an inline fuse, and I had that done, but the original switch remains. I can't see any external signs of failure, like fluid leak. Can't tell if the thing even works at all, because it's a backup, and the primary sensor for cc disengagement is the switch on the brake pedal - which is fine. Guess I could test it by disconnecting the brake pedal switch, but who wants to be on the highway with disabled brake lights? The switch is just $25 on Amazon, but I hate to throw money at a problem. I could check it by stepping on the pedal, but what will this tell me? If anything it randomly senses pressure when there isn't any. Any ideas?

 

[DR98FL]

I have a 98 Sport SOHC 4.0 V6 with cruise control controls only, on my steering wheel. No radio controls.

Do you have any working brake lights? All the brake signals used by the Explorer uses the same brake pedal position switch.

The brake pressure switch on the end of the master cylinder works like this. The brake pressure switch has continuity to the CC servo when the brakes are not applied. When the brakes are applied it breaks the connection and removes the 12 volt signal to the CC servo. Check this with a multimeter.

The wire with the inline fuse harness that Ford added,should have 12 volts constant power. Check this.

DR98

 

[1998Exp]

I have a 98 Sport SOHC 4.0 V6 with cruise control controls only, on my steering wheel. No radio controls.

Do you have any working brake lights? All the brake signals used by the Explorer uses the same brake pedal position switch.

The brake pressure switch on the end of the master cylinder works like this. The brake pressure switch has continuity to the CC servo when the brakes are not applied. When the brakes are applied it breaks the connection and removes the 12 volt signal to the CC servo. Check this with a multimeter.

The wire with the inline fuse harness that Ford added,should have 12 volts constant power. Check this.

DR98

Thanks for your advice!
Brake lights are fine.
The problem with the cc is intermittent, so I will shake the wires on the connector and along the added harness, to see if the 12V going to the servo through it disconnects (a test light should be better at detecting a momentary break than a DVM). Don't know if the inline fuse that they added is replaceable or soldered - perhaps it has a loose contact. For now Amazon is not getting my $20 -- at least not for this

 

[C420sailor]

I’m curious as to why the self test doesn’t work. That’s weird.

How does it disengage while using the buttons? Does pressing OFF immediately disconnect the CC?

My 99 has the electronics package, and some corroded buttons on the CC board in the steering wheel switch housing were to blame. It also wouldn’t enter self test mode. Replaced the switch assy and everything works great now.

 

[1998Exp]

I’m curious as to why the self test doesn’t work. That’s weird.

How does it disengage while using the buttons? Does pressing OFF immediately disconnect the CC?

My 99 has the electronics package, and some corroded buttons on the CC board in the steering wheel switch housing were to blame. It also wouldn’t enter self test mode. Replaced the switch assy and everything works great now.

I was surprised to find out, years ago, that the self-test did not work. All the switches worked (and still work) properly - back then I even checked connectivity through the clock spring. My guess was that the reason was the totally different set of switches on the steering wheel in the Limited trim (if you are not familiar with that, they also control cabin temperature, blower speed and several radio functions). I might have also done something wrong back then -- haven't tried again. The current intermittent disengagement does not look like something that would be detected by the self test anyway.
Pushing OFF disconnects immediately, like it should. There is, of course, a chance that this switch is defective and occasionally sticks, but one would think that this will just prevent the cc from engaging, not disengaging randomly. It now hasn't happened for a couple days, so will take a while to get to the bottom. Will post what I found when there is progress.

 

[C420sailor]

In the factory service manual (available in pdf online) there is a great troubleshooting procedure. I used it to diagnose bad switches.